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TlUnn EDJTinN. ■ 





In issuing a third edition of this book it appeared 
advisable to reconstruct and enlarge it in order to 
introduce new material which had become avail- 
able. The original form of lectures as delivered 
to a class of students has been abandoned and the 
book rewritten and brought up to date. 

No attempt has been made to give a historical 
review of marine propulsion, and of the innumer- 
able forms of screw proposed since 1836, only 
those are described which embody some intelligent 

The table of constants for disc-area and revolu- 
tions on p. 73 will, I think, be appreciated by those 
who have many screws to design. The complete 
series of model experiments upon which it is based 
is the work of Mr. R. E. Froude, and I am indebted 
to him for permission to make use of it. 

There are many ways in which it is possible to 
tabulate experimental results, but after much con- 
sideration I believe that the table of constants 
which I have here given is the best that can be 


devised, being independent of scale and equally 
accurate for all sizes of propellers. It is possible 
by means of it to design a screw which shall have 
maximum efiBciency under any given conditions of 
indicated horsepower and speed ; or if revolutions 
or diameter are so limited as to preclude the adop- 
tion of the most suitable dimensions, those may be 
selected which will be the best under the given 
conditions and the efficiency at once ascertained, 
provided only that the vessel is of such a form that 
the propulsive coefficient is not abnormal, and that 
the designer can correctly estimate the speed of 
the following current in which the screw works. 
More than this I do not think can be reasonably 
expected. No table can supply the place of judg- 
ment and experience. 

Sydney W. Barxaby. 

The Hollies, Chiswick Mall, W. 
September Uth, 1891. 



In preparing these lectures for the students of the 
Royal Naval College, I availed myself of informa- 
tion from various sources. 

Now that they are published verbatim in book 
form, it becomes a duty as well as a pleasure to 
acknowledge the assistance thus received. 

I am indebted first of all — and who that studies 
the subject of Marine Propulsion is not? — to 
Professor Rankine. Also to Mr. W. Froude, Mr. 
Bourne, Mr. White, Professor Osborne Reynolds, 
Mr. Sennett, Mr. Maginnis, and Mr. Seaton. 

There is, however, much that is new. 

The curves in Plate II., which enable the dia- 
meter, pitch, and speed of revolution of a screw 
suitable for any horsepower and any speed to be 
determined, are now made public for the first 

For most of the new material, and especially for 
permission to publish these curves, and the method 
of producing them, I am indebted to Mr. Thorny- 


It was my privilege to be associated with him 
in making some 550 experiments with model 
screws, and a (Considerable portion of these lectures 
is the result of knowledge thus obtained. 

I feel some diflBdence in putting forward in my 
own name information so acquired, as the credit of 
it is entirely due to Mr. Thornycroft, but after this 
explanation, any merit which may be found in the 
following pages will be attributed to the proper 

Sydney W. Barnaby. 

The Hollies, Chiswiok Mall, W. 
October 12/A, 1885. 



I HAVE purposely adhered to the original form 
of these lectures in preparing a second edition, 
although they are not so well arranged as they 
might have been, had they been written with a 
view to future publication. 

With the exception of such textual corrections 
as were necessary, by reason of errors which had 
been overlooked in the first edition, they remain 
as they were delivered, and are largely supple- 
mented by Notes in an Appendix. 

I have to thank several correspondents who 
have pointed out some of these errors, and I shall 
be glad to be informed of any remaining un- 

I am especially indebted to Mr. C. H. Wingfield, 
Assoc. M. Inst. C.E., for his careful revision of the 
new edition. 

Sydney W. Barnaby. 

The Hollies, Chiswick Mall, W. 
January lOth, 1887. 



First Puinoiples .. .. .. .. 1 

The Paddle- wheel .. 6 


.1. HE oOHE W •• •• •• at •• x^ 


Experiments with Models and their Applioatton to 
THE Determination of the most suitable Dim en- 

BIONS •• •* t. •• .• •• OJL 

Geometry of the Screw .. .. 75 

The Htdraulio Propeller .. .. .. .. 94 

The Sorew-turbine Propeller .. .. .. ..105 

XNDKlk .. .• .• •• <* «• «( XXX 




irly all marine pro- 
of a mass of water 
it of the required 

f water acted upon 
' second = W, and 
ot per second im- 
1 water = S, tlien 
lie propelling force 

is — . I" second : and this 

is independent of the form ui ^ /opelling apparatus 
altogether. S is commonly known as the real 
slip, but will here be generally referred to as the 
rate of acceleration, or more shortly •'is the accele- 

When the vessel is in motion at a regular 


speed the reaction — is equal to the resistance. 





Page ly, line 16, for "PR" read "PR -V." 

18 where ^ = 32*2 feet per second; and this 

is independent of the form of propelling apparatus 

altogether. S is commonly known as the real 
slip, but will here be generally referred to as the 
rate of acceleration, or more shortly as the accele- 

When the vessel is in motion at a regular 

speed the reaction ig equal to the resistance. 





The principle upon which nearly all marine pro- 
pellers work is the projection of a mass of water 
in a direction opposite to that of the required 
motion of the vessel. 

If the weight of the mass of water acted upon 
by the propeller in pounds per second = W, and 
if the sternward velocity in feet per second im- 
parted to it in relation to still water = S, then 
the reaction which constitutes the propelling force 

is where ^ = 32*2 feet per second; and this 

is independent of the form of propelling apparatus 
altogether. S is commonly known as the real 
slip, but will here be generally referred to as the 
rate of acceleration, or more shortly as the accele- 

When the vessel is in motion at a regular 

speed the reaction is equal to the resistance. 


,V • V 


So long as there is a resistance to be overcome by 
the propeller, there is no possibility of reducing 
the real slip or acceleration S to zero, except 
by making W, the weight of water acted upon, 

When a propeller is to be designed for any 
given set of conditions, it is of the first importance 
that the relation between the mass of water acted 
upon and the acceleration imparted to it should be 


such that while the product — = — shall equal the 

estimated resistance of the ship, and the size and 
rate of motion of the propelling apparatus such 
as shall suit the conditions of the case, the 
economic result may yet be the best attainable, 
or may only fall short of the maximum by an 
£fcViqunt which is calculable^ and which it may 
be desirable to sacrifice in order to obtain other 

The method of calculating the propulsive eflfect 
of the screw from the backward slip is that 
adopted by Rankine. Professor Greenhill has 
published some able papers on the theory of the 
screw,* in which he determines the propulsive 
effect as due to the reaction of the water to the 
rotatory motion given to it in the wake, and 
Professor FitzGerald has shown f that if the 
motion imparted to the water by a particular 

* Trans. Inst. Naval Architects^ xxix. p. 819. 
t Engineer^ August 22 and September 19, 1890. 


screw is assumed to be a certain form of vortex, 
and a calculation be made of the power absorbed 
in producing such a vortex, it will be found to 
agree very well with the actual horsepower put 
through the screw. It is to be hoped that light 
will be thrown upon some remaining obscurities 
in the action of the screw by these independent 
investigations, but as they lead to the same con- 
clusions as the older treatment, and as the latter is 
simpler and of more general application, it has 
been thought best to adhere to it. 

Rankine has defined * the theoretical limit 
towards which the efficiency of propellers may be 
made to approximate by mechanical improvements, 
and has pointed out certain causes which make 
the actual efficiency fall short of that limit. He 
states that " if the propelling instrument be so 
constructed as to act upon each particle of water 
at first with a velocity equal to the velocity of 
feed " — that is the speed of the water entering the 
propeller — '' and gradually increasing at a uniform 
rate up to the velocity of discharge, then the loss 
of work is the least possible." The oar, when a 
uniform force is applied to it by the oarsman 
throughout the stroke, approaches closely to this 
limit, as does also the screw-turbine propeller. 
(See p. 108.) . 

There is a certain quantity of work which 

* Engineer, 1867, xxiii. p. 25 ; and * Miscollanoons Scieutifio 
Papers,' edited by W. G. Miller, p. 54.4. ^ 

B 2 


must be lost under all circumstances, and it is 
equal to the actual energy of the discharged water 
moving astern with a velocity S relative to still 
water. As this energy varies as the weight 
multiplied by the square of the velocity, if the 
quantity of water acted upon is doubled the loss 
from this cause is doubled, but if the acceleration 
is doubled the loss is increased fourfold. This 
explains why the hydraulic propeller, which is 
forced to act upon a much less area of column 
than the screw, appears at such a disadvantage 
when compared with it. 

The causes of loss of work in propellers of 
diflferent kinds may be thus summed up: — 1st, 
Suddenness of change from velocity of feed to 
velocity of discharge. The radial paddle-wheel 
is defective in this respect. The feathering wheel, 
the screw, the Ruthven pump, and the oar are 
more or less exempt. 2nd, Transverse motion 
impressed on the water. Propellers which lose 
in efiBciency from this cause are ordinary screws, 
which impart rotary motion ; radial wheels, which 
give both downward and upward motion in 
entering and leaving the water ; and oars, which 
impart outward and inward motion at the com- 
mencement and end of the stroke respectively. 
This loss is greatly reduced in the screw-turbine, 
and may be entirely avoided in the hydraulic 
propeller.. 3rd, Waste of energy of the feed 
water. This is experienced by the hydraulic 


propeller only as generally applied, and has been 
one of the causes of its ineflSciency. It is not, 
however, a defect inherent to it, and has been 
avoided in some later applications. 




As a propelling instrument the paddle-wheel 
is not inferior to the screw, but its speed of 
revolution is necessarily slow, and paddle engines 
are therefore larger, costlier, and heavier than 
screw engines of the same power. Until the 
introduction of the screw-turbine, it was the only 
propeller used for vessels of very shallow draught. 

In order to ascertain the comparative value of 
the paddle and screw for towing purposes, H.M.S. 
Rattler and Alecto, the former a screw and the 
latter a paddle vessel of the same size and power, 
were lashed stem to stern. The Battler towed 
the Alecto astern against the whole power of 
her engines at the rate of 2*8 knots per hour. 
Almost as much power can be developed with the 
screw when the vessel is towing as when she is 
running free, but this is not the case with the 
paddle-wheel. The engines of the Alecto could 
not get away, and were only able to develop 140 
I.H.P., while the Battler was developing 300. 

It is difficult to frame rules for determining 
the proper area of floats for a given I.H.P. and 
speed of vessel, because so much depends upon 


the position of the water surface in relation to the 
wheel when the vessel is at full speed. 

There is usually a wave hollow in way of the 
wheel due to the motion of the vessel, and the 
action of the paddles is to cause the water to run 
towards them, and to produce a still greater de- 
pression of level in front of and below the wheel. 
Unless the vertical position is properly arranged 
the immersion of the floats will be insuflBcient at 
fiiU speed, and the slip will be excessive. It is 
the practice of at least one eminent firm of ship- 
builders to make model experiments in a tank, 
with the wheel in place, and revolved by clock- 
work at the proper speed, in order to ascertain 
the amount of the depression. The usual course 
followed in designing the wheels for a new vessel 
is to work from the nearest type, within the builder's 
experience, which has given good results. 

Rankine gives a method of calculating the 
effective sectional area of a pair of feathering 
floats, which depends upon the general proposition 
already stated (p. 1), and which is common to all 

If V = speed of vessel in feet per second ; 
* S = speed of centre of float relatively to 
the water in feet per second ; 
A = area of a pair of floats in square feet ; 
R = resistance of the vessel in pounds. 

. s - — i-O^I— - V 

100 - % of Blip 


Then, since R = (see p. 1), 


_ 64 xA(V -1.8)8 

.•.A= « 

2 ( V -h S) S 

The formula is useful for purposes of com- 
parison, as showing how the eflfective area varies 
with power, speed, and slip, and it should give a 
fair approximation to the area of float immersed 
at full speed ; but as it is usual to make the top 
edge of the lowest float about awash when the 
vessel is at rest, the width will be increased above 
that theoretically necessary by an amount equal to 
the fall of water-level at the wheel. 

In applying this formula to radial wheels, S 
should be taken as the speed of the lower edge of 
the float. 

In radial wheels the number of floats should 
equal the number of feet in diameter, and the 
breadth of a float is usually from f inch to one 
inch for each foot of diameter. In a feathering 
wheel the floats should be half as numerous and 
twice as broad as the floats of a radial wheel. 
The width of the wheel should be from one-third 
to one-half the breadth of the ship. 

The diameter of the wheel is determined by 
the intended speed of the ship, the slip, and the 
number of revolutions considered most suitable, 






generally from 20 to 30 per minute, but some- 
times as many as 50. 
Example : — 

Speed of ship 15 knots = say 1500 ft per minute. 

Slip 16 per cent. = say 800 

.-. Circumferential velocity of wheel = 1800 
Reyolutions 80 per minute. 

Diameter = rr-m t^z =19 feet. 

3'14 X 80 

The diameter would be taken at the centre of 
floats in a feathering wheel. 

Fifteen to twenty per cent, is an average slip. 
The floats of a feathering wheel are constructed 
to cleave the water without shock. If a, Fig. 1, 

Pio. 1. 

represents the direction of motion of a descending 
float, and the distance moved through by it in a 
given time if the vessel were stationary, and b 
equals the travel of the ship in the same time, then 
the actual path of the float is represented by the 



resultant. The plane of the float entering the 
water should coincide with this line. It is found 
that if a circle B F D, Fig. 2, be drawn through 
the centres of the floats, lines from the summit F 
to the points of intersection with the water-line B D 
will generally give the direction of the floats with 
sufficient accuracy. Levers, the lengths of which 
are about three-fifths of the depth of the float, are 
fixed perpendicularly at their centres B6, C(?, Drf. 
The centre of a circle, in the circumference of 
which the ends bed of these three levers lie, is 
the centre of the excentric wbicb produces the 
required motion of the floats. Fig. 3 represents 
the wheels of a vessel built by Messrs. Napier, 
Shanks, and Bell, and engined by Messrs. Rankin 
and Blackmore, of Grreenock, to whom we are 
indebted for the illustration. The dimensions of 
the vessel are: — length, 260 feet; beam, 28 feet; 
draught, 5 feet 9 inches. The I.H.R was 2680, 
and the speed 18 i knots. The diameter of the 
wheel is 20 feet 6 inches over the floats, which are 
made of straight elm 9 feet 9 inches by 3 feet 6 
inches. The revolutions were 47 per minute, and 
the slip 26^ per cent. The lowest float was im- 
mersed one inch from the top edge when at rest. 
The slip is rather high, and it is probable that a 
still better performance would have been obtained 
if the wheel had been rather more immersed. 





Three strings wound spirally round a cylinder 
make a three-threaded screw. If instead of strings 
flat blades be wound edgewise, each having an 
edge soldered to the cylinder, then if a slice be cut 
off as shown in Fig. 4, there will be one piece of 

Fig. 4. 

blade attached to the slice if the screw have one 
thread, two pieces if two threads, and so on. 

The "length of the blade" is equal to the 
length of the slice thus cut off, and the length of 
the cylinder necessary to contain one complete 
convolution of the blade is the " pitch " of the 
screw. The ratio of the length of the blade to 
the pitch is called the " fraction of pitch," a term 
more in use on the Continent than in this country. 

It will be seen that the '' pitch " of the screw 
has to do only with the form of the helix itself. 



and has nothing to do with the velocity which 
may be imparted by it to the water. Theoretically, 
the blade is supposed to be of the form of a thin 
plate, as shown in Pig. 4, of equal thickness 
throughout and with both faces alike. The side 
of the blade which presses against the water when 
propelling the vessel ahead is called the " front " 
or " driving face " ; the opposite side is the " back " 
of the blade. When speaking of the screw as a 
whole the nomenclature is commonly reversed, 
"in front of the propeller" standing for forward 
of the screw in relation to its position on the 
vessel, and " behind the propeller " meaning abaft 
it. These terms " in front " and ** behind," which 
are apt to be confusing, will be avoided in this 

Fig. 5. 

Fig. 5 shows a screw of " expanding or '' in- 
creasing " pitch as originally proposed by Wood- 
croft. The length of cylinder necessary to contain 


a complete convolution is not the same at all 
parts, and the pitch therefore is " variable." The 
first turn of the thread has a pitch equal to the 
length a b ; the second has a louger pitch equal 
to 6e. If a slice be cut off the cylinder (repre- 
sented in Fig. 5 by the screw-shaft) midway 
between a and 6, and of any length, it would be 
said to have a mean pitch equal io ah, A slice 
taken at a position midway between b and c 
would be said to have a mean pitch equal to 6 (?, 
and similarly for any other part. 

The edge of the blade which first meets the 
water is called the " forward " or " leading " edge, 
distinguishing it from the " after " or " trailing " 

The *' disc area '' is the a^ea of the circle swept 
by the blade tips.* 

The " developed area " or " blade surface " is 
the sum of the areas of all the blades, exclusive of 
the boss. 

The *' projected blade area " is the sum of the 
areas of the blades, exclusive of the boss, pro- 
jected upon an athwartship plane. 

(It is convenient to use a term expressing the 
relation which the product of the pitch and revo- 
lutions of the screw per minute bears to the ad- 
vance of the vessel through the water per minute. 
This term is *' apparent slip." 

* Eankine uses '* effective disc area," which is the area 
exclofiiye of the area of the boss, but it is now usual to measure 
disc area as defined in the text. 


If P = mean pitch ; 

R = revolutions per minute ; 

V = speed of ship in feet per minute ; 

PR — Y 
then — ^^D~^ X 100 = percentage of apparent 
P R 

slip. In the great majority of cases P R is greater 
than V, but it is occasionally equal to or less than 
V. The apparent slip is positive, nil, and negative 
in the three cases respectively. The real slip or 
acceleration of the water S (see p. 1) is not measur- 
able from the pitch and revolutions of the screw. 
A propeller placed at the stern of a vessel is in a 
current having a forward mean velocity IT rftlativft 
to still water caused by the friction of the skin of 
the vessel. While the vessel advances at a velo- 
city Y through the water, the ^^rew g^(^yftT]( ^ftg at a 
less velocity = Y — U. If the apparent slip is nil 
then the real slip of the screw is equal to U. Con- 
ceive a propeller of increasing pitch which shall 
be so designed that the pitch of the forward edge 
multiplied by the revolutions per minute shall 
be equal to the speed of the propeller through 
tlie water, that is Y — U, and the pitch of the 
after edge multiplied by the revolutions equal 
to Y, then the mean pitch, as already ex- 

plained, would be called 1- :. The late 

Mr. Froude showed that under these circumstances 
apparent negative slip is possible. He describes 
an ideal case in which the whole of the resistance 


of a vessel consists in skin friction, wave-making 
and other factors being excluded. The dynamic 
equivalent of the propulsive force employed in 
keeping her in motion is found in the frictional 
wake, and a propeller which should pervadingly 
operate upon the wake in such a manner as to 
bring it gradually to rest, would, in thus neutralising 
it, maintain the propulsive fprce, and, given esta- 
blished motion, a theoretically perfect propeller, 
quite clear of the ship's stern, would maintain that 
motion and exhibit apparent negative slip equal to 
half the forward mean velocity of the wake at the 
point where the propeller operated. 

In this case it is clear that apparent negative 
slip results from the fact that while a sternward 
velocity is supposed to be imparted to the water 
equal to the product of the number of revolutions 
multiplied by the pitch of the after edge of the 
screw, the mean pitch of the screw itself is nomi- 
nally less than the pitch of the after edge. Nega- 
tive slip would disappear in this particular case if 
the speed of advance of the screw were calculated 
from the after pitch instead of from the mean. 

Apparent negative slip is sometimes exhibited 
by screws of uniform pitch when the ratio of 
pitch to diameter is small. The twin screws of 
H.M.S. Colling icoody with a pitch-ratio of 1*6, 
gave 1 ' 26 per cent, apparent negative slip, and 
this was increased to 2*56 per cent, when the 
pitch-ratio was reduced to 1. 

Tiii^: sciiEW. 17 

Numerous explanations have been given of the 
phenomenon of apparent negative sh'p, but none of 
them can be accepted as satisfactorily accounting 
for its occurrence in the case of well-formed uni- 
form-pitch screws, the pitch of which has been 
carefully verified as in the case of the Collingwood. 

It has been suggested that the blades twist or 
spring under the pressure of the water, which 
would have the effect of increasing the pitch, and 
that they recover their shape when the pressure is 
relieved, so that measurements taken after the trial 
even would be misleading. 

If this were the case screws with thin blades 
would be most likely to show negative slip, 
but it is, on the contrary, generally met with 
in screws with very thick blades where springing 
would be least likely to occur. Moreover, it 
might be expected that the metal would soon give 
way by fatigue if it were distorted by the pres- 
sure, as the fluctuations are very great and very 

What has been said about the effect of thick 
blades lends force to another suggestion, which is 
that it may be attributed to the effect of the round 
back of the blades. It has been explained, p. 13, 
that pitch is measured on the assumption that both 
sides of a blade are alike. The effect of the round 
back of the blade must be to increase the effective 
pitch and to tend to reduce the apparent slip, 
although it is difficult to say by how much, and it 



is not, in the author's opinion, sufficient to account 
for the CoUingwood results. 

It has been pointed out that the iatermittent 
action of the blades passing through the dead water 
abaft the stern-post of a full formed ship reduces 
apparent slip and may even cause it to change 
sign, but this does not afiFect the case of the ship 
referred to, which is a fine ship, and the screws 
being twin, are not behind a stern-post. 

Another suggestion has been that the motion of 
the particles in the wave which followed and enve- 
loped the stem of the ship might produce apparent 
negative slip. All attempted explanations based 
upon the effect of dead water and following current 
alone, apply only to a screw of increasing pitch, 
and this has already been dealt with (p. 16). 
They are quite inapplicable to a screw of uniform 
pitch, and the same thing is true of the theory 
based upon the circular motion of the particles of 
water in waves. The waves referred to are pre- 
sumably those made by the vessel, because it can- 
not be contended that negative slip results from 
the screw working among free waves. It is well 
known that the contrary effect is produced, the 
slip is increased, and the most favourable condition 
for the exhibition of apparent negative slip is still 
water. If a wave follows the ship, and its energy 
can be made use of in any way by the screw, that 
wave has previously been created by the ship from 
which the energy has been robbed, and can be only 


partially restored. Could it all be given back, and 

could the whole of the energy of the frictional wake 

be utilised by the screw without loss, there would 

still be no surplus thrust to keep the vessel in 

motion. It is certain that there must be a stream 

of water left behind by the screw having stemward 

motion relative to still water. How is it then that 

notwithstanding this necessity, apparent negative 

slip is occasionally obtained with screws of uniform 

pitch ? In a paper read before the Institution of 

Civil Engineers on the screw propeller,* the author 

gave what seems to him a satisfactory explanation 

based upon a proposition recently enunciated by 

Mr. R. E. Froude,f to the effect that the slip or 

acceleration S of the water in the race was always 

in excess of the slip of the screw [P R: vMr. Froude 

showed that if no rotation were produced in the 

race by the propeller, a limiting case was reached 

in which one-half of the whole acceleration would 

be produced forward of the propeller and one-half 

aft of it. The water forward of the propeller was 

aflfected before it was actually in contact with it, 

and would run towards the screw, meeting it with 

a velocity, as regards still water, of o, and the 

action of the propeller upon the water while in 

* * Proceedings of the InBtitution of Civil Engineers,' cii. 
p. 74. 

t * Transactions of the Institution of Naval Architects/ 1889, 
p. 390. 

C 2 


contact was to accumulate pressure which had the 

effect of increasing the acceleration of the race 

after it had left the propeller. This is perhaps 

more easily understood if we suppose the propeller 

to be stationary in an ocean moving with a velocity 

V. At some distance forward of the propeller the 

water will be advancing to meet it at a velocity V. 

On nearing the propeller, the water is accelerated 

by its sucking action, and meets it at a velocity 

V + -5. The length of the blades may be supposed 

to be so small that no appreciable change in velo- 
city can take place in the stream while actually 
passing through them, but after leaving them the 
speed of the stream is further accelerated up to the 
final speed Y + S. The mean speed of stream in 

which such a propeller works is therefore V + 5 

and the real slip of the propelling apparatus, which 

is a measure * of its efficiency, would be 5, but the 

speed of the race is Y + S, and the real slip of the 
water is S. Such a propeller might show a con- 
siderable amount of apparent negative slip if placed 
behind a ship and in a following current, a condi- 
tion which is of course essential, as if it were pro- 
pelling a phantom ship (see p. 58) the apparent 

slip would be the same as the real slip, viz. — . 

It is impossible to make an open screw which 


shall not rotate the water, but the finer the pitch is 
the less the rotation will be. 

Mr. Thornycroft has shown that the relation 
between the amount by which the race is accele- 
rated forward and aft of the screw respectively may 
be expected to depend upon the amount of the 
rotation produced. A screw of coarse pitch-ratio 
which will rotate the race considerably, will pro- 
duce a large proportion of the whole acceleration 
before the water reaches the screw, leaving only a 
small part to be imparted abaft it. When the 
rotation is a maximum, tlie whole acceleration is 
produced by suction, and the speed of the stream 
on meeting the propeller is V + S, in which case 
the real slip of the screw is equal to the real slip of 
the water S. All open propellers, by which is 
meant propellers which are not confined in a casing 
like the screw-turbine, occupy some intermediate 

position, and are working in a stream with a velo- 

city varying between V+ S and V+^, depending 

upon the greater or less rotation of the race. 
Hence the finer the pitch-ratio the more favourable 
would be the conditions for obtaining apparent 
negative slip, and it is found to be invariably the 
case that it only occurs under these conditions, and 
that it may be increased by still further reducing 
the pitch of screws exhibiting it (see p. 16). 

There are a number of pitchometers made which 
will measure the pitch of a screw with sufficient 


accuracy if it is uniform. They are not to be 
depended upon for the measurement of increasing 
pitches. The operation may be performed without 
instruments, as follows : — 

Strike an arc of a circle a h, Fig. 6, concentric 
Pj^ ^ with the axis of the propeller, 

upon one of the blades with 
any radius B. Divide the arc 
into a number of equal inter- 
vals, as 1, 2, 3, 4, 5. Measure 
off the same number of in- 
tervals upon a base>line xy, 
Fig. 7, making them equal to 
the developed length of the 
intervale upon the arc. Mea- 
sure the ordinates at each in- 
terval on the arc from a plane 
perpendicular to the axis of the propeller, and lay 
off the ordinates 1 1', 2 2', 3 3', &c., at the corre- 

sponding intervals on the base-line. Draw a line 
CD through the points 1', 2', 3', &c., and produce 



it to cut the base in C. If the pitch is uniform 
C D will be a straight line. Measure off from C a 
length OE equal to the circumference of the circle 
of R radius, and erect a perpendicular at E cutting 
C D at F. E P is the pitch of the screw. If the 
pitch is not uniform the points 1', 2', 3' will lie in 
a curve. Tangents must be drawn to the curve 
at the extremities 1' and 5', and the pitch of each 
measured separately, see Figs. 8 and 9, and the 

Via. 8. 

mean of the two will be the mean pitch of the 
screw. Measurements should be made of each 
blade and at a number of different radii, and the 

24 M AH INK PliO PELL Ens. 

mean of all the readings taken as the mean pitch. 
If the i^itch is uniform, and great accuracy is not 
required, choose any two points on the arc ah, 
Fig. 6, such that radial lines from them to the 
axis subtend an angle of 30°. The dijQFerence 
between the length of the ordinates of these points 
to a plane at right-angles to the axis, measured in 
inches, is equal to the pitch in feet. 

The pitch of small model screws used for experi- 
mental purposes can be most readily obtained as 
follows : — Make a cylinder of wood of a diameter 
about two-thirds that of the propeller. Fit a short 
mandril to represent a piece of the shaft into the 
boss, and pass the mandril through a hole in the 
axis of the cylinder which has been bored to fit it. 
Wrap a sheet of paper round the cylinder, securing 
it with an elastic band, and cut the edge accurately 
to fit the face of the blade. The direction of the 
axis F E should be marked upon it. When the 
paper is taken off* the cylinder and unrolled, the 
edge which fitted the face of the blade will form a 
straight line as C F, Fig. 10, if the pitch is uniform, 
and if D be the diameter of the cylinder, then 

rr-p: =-Yr ,<—.-:. If thc Wadc is not of uniform 

C E D X 314 

pitch it will form a curved line, and the pitch of 

the leading and after edge must be obtained by 

drawing tangents to the extremities of the curve 

as already described. 

It is sometimes useful to be able to estimate 



roughly the pitch of a screw at sight. This may 
be done by observing at what radius the Wade 
makes an angle of 45° with the axis ; the pitcli is 
Cfjual to the circumference at this radius. 

Fir,. 10. 

The screw was brought into successful operation 
as a propeller by Ericsson and Smith in 1836. 
The Archimedes^ a screw vessel of 237 tons 
burden, was built by the latter in 1839. The 
screw used was a single threaded helix of one 
complete convolution. A double thread of half a 
convolution was afterwards tried and found to be 
an improvement ; but the best result was obtained 
with two threads and one-sixth of a convolution. 
The Earl of Dundonald in 1843 patented a pro- 
peller with the blades thrown back as shown in 
Fig. 11, the object being to counteract centrifugal 
motion of the water, supposed to be caused by the 
rotation imparted to it by the screw. 

When a propeller is not sufficiently immersed to 
prevent it from drawing down air, it is probable 
that centrifugal action takes place, and that the 
column of water takes the form of a cone with the 


screw for an apex ; but when no air gets to the 
propeller, observation of its action in the phospho- 
rescent water of tropical seas appears to show that 
an ordinary screw does not disperse the water, but 

Fig. 11. 


projects a column more or less cylindrical, and 
having the appearance of a twisted rope, the 
strands of which unravel themselves as they pass 

In 1849 Robert Griffiths patented a self-govern- 
ing propeller, which he thus describes : — "If the 
screw moves with greater velocity than usual, the 
increased resistance of the leading edge shall 
correspondingly increase the pitch, thus increasing 
the resistance and bringing down the revolutions." 

The propeller chiefly associated with his name is 
shown in Fig. 12, which represents the form now 
adopted in the British Navy. The principal 
feature in the Griffiths screw is the large boss, 
which, while not impairing the efficiency, enables 
the blade to be fixed in such a manner that the 

* See a paper by M. Marchal in the * TraDsactions of iho 
Institute of Naval Architects,' 1886, xxvii. p. 288. 


pitch can be readily altered. This is an important 
consideration, ae it is difficult to fix upon exactly 
the right pitch in designing a propeller to run at a 
given number of revolutions. 

The Hirech screw is shown in Fig. 13. It has 
an increasing pitch, and the propelling surfaces are 
so formed as to throw the, water somewhat towards 
the axis. 

The Mangin propeller, Fig. 14, eonsista of two 
narrow-bladed screws set behind one another on 
the screw*ehaft with a space between them. It is 
supposed not to rotate the water so much as other 



Rigg's propeller had a fixed screw or guide- 
blades placed behind the revolving screw, with the 
blades set at the reverse angle, so as to take the 

Fig. 13 

rotation out of the water and leave it moving* 
directly astern. Rankine and Napier patented a 
modification of this idea in the form of a twisted 
rudder, of which the part above the screw-shaft 
bends in one direction and the part below in the 

Screws have been tried with the pitch in the 
centre less than the pitch at the circumference, so 
as to allow the central part simply to follow up 
the water. 



' The Thornycroft screw, Fig. lo, which has 
proved very successful, has an increasing pitch at 
the middle of the blade, but it gradually becomes 

Fio. 14. 

uniform towards the root and towards the tip, the 
reason being that at the root the rotation is already 
excessive, and it is consequently not advisable to 



increase it by increasing the pitch, and towards the 
tip, if it is attempted to accelerate the water too 
much, it escapes round to the back of the blade. 

Fig. 15. 

The blades are also thrown back after the fashion 
of the Dundonald propeller, but, instead of being 
straight, they are convex on the driving face. 

An ingenious attempt to make use of a certain 
amount of energy said to be wasted by the screw 
has been made recently by MM. des Gofifes and de 
George. The inventors say that the viscosity or 
resistance to rupture of the water in which any 
helical propeller revolves, causes an appreciable 
current to be set in rotation just beyond the tips of 
the screw-blades. It is contended that a series of 
helical surfaces, opposed in direction to those of the 
screw proper, will receive a thrust from the revolv- 
ing ring of water, which can be utilised for pro- 



pulsion. The '* Antispire," as it is called, can be 
placed around a propeller of any form. It is shown 
in Fig. 16. The only experiments with the appa- 
ratus which the author has witnessed were made 

Fig. le. 

in a tank, and as there was no motion through the 
water it was not possible to tell how much the 
result would be affected by the friction of the ring 
itself, but a large increase of thrust was found to be 
produced by it, and it is possible that the friction 
of the surfaces would be more than counterbalanced 
and a real propulsive force exerted. It is reason- 
able to suppose that there is an unutilised reservoir 


of wprk in revolving currents external to the pro- 
peller disc. Rings or bands without helical blades 
have been used for protecting screws and for giving 
increased manoeuvring power, but these plain 
rings do not increase the thrust or the efficiency of 
the screw, and the addition of the blades would 
certainly be found advantageous in such cases, and 
may be worthy of a still wider application. 

In some double-ended ferry-boate, both in this 
country and America, screws have been placed at 
both ends of the vessel, for what appear to be 
suflScient reasons connected with the service which 
they have to perform. In the well-known Mersey 
boats there are four screws, but in a new ferry- 
boat, the Bergen^ built in America, two only are 
employed, one forward and one aft, driven by the 
same shaft — an arrangement which appears to be 
inferior. The forward screw of the Bergen is 
estimated to augment the resistance of the hull by 
23 • 5 per cent., and its propelling efficiency is only 
43 per cent, of that of the after screw. 

There is no doubt that the best position for a 
screw is at the stern. As a vessel moves through 
the water the friction of the sides and bottom 
imparts motion to a layer of water which increases 
in thickness towards the stern, so that a consider- 
able quantity of water is left with a motion in the 
same direction as the vessel. If the screw works 
in this water it is able to recover some of the 
energy which has been expended by the ship in 


giving it motion. The speed of this wake, which 
Rankine estimates may be as much as one-tenth of 
the speed of the vessel, depends not only upon the 
form, but upon the nature and extent of the sur- 
face. It would not be desirable to increase the 
volume or the velocity of a wake for the purpose 
of improving the efficiency of the propeller, be- 
cause this very surface friction proves to be the 
largest portion of the resistance of a ship at 
moderate speed; but as it is a necessity that 
there should be a wake, it is a distinct advan- 
tage to place the propeller in it and allow it to 
utilise as much as possible of the energy it finds 

This frictional wake must not be confused with 

deag water, which is water eddying behind a bluff 
stern, an3 whicb has acquired the full velocity of 
the vessel. When once the speed of the vessel has 
been imparted to this water, not much energy is 
wasted in maintaining it. If it is drawn out by 
the screw, fresh water must take its place, and 
there will be a continual drain of energy from the 
ship, as the inflowing water must in its turn have 
the full forward velocity imparted to it. Dead 
water is almost a thing of the past, and is met 
with only in the case of very full ships. 

If a screw is placed behind a stern so bluff that 
the supply of water is impeded, it will draw in 
water at the centre of the driving face, and throw 
it off round the tips of the blades like a centrifugal 



pump. The effect upon the ship is then peculiar. 
Sir Frederick Bramwell has described a vessel 
which went astern whichever way the screw was 
driven, the reason being that a very bluff stern 
caused the screw to act as described, and a loss of 
pressure was produced upon the stem of the 

It is very important that a propeller should 
have sufficient immersion, since if it breaks the 
surface of the water the efficiency is reduced to a 
remarkable extent (see Plate 1) ; but if it is suffi- 
ciently far below the surface to prevent it from 
drawing air, any further immersion within the 
limits that can practically be obtained is of little 
value. The speed with which water can follow 
up the blades of a screw depends upon the head 
of water over them, but when air is excluded the 
equivalent of a head of 30 feet is supplied by the 
atmosphere, and this being elastic and having 
practically no inertia to resist sudden motion, its 
pressure is more effective than that of a column 
of water of equivalent weight. 

It is probable that the inequality in the onward 
motion of the layers of water forming the frictional 
wake, accounts to some extent for the vibration 
caused by the screw, since each blade in revolving 
meets with an alternately diminished and increased 
resistance. An ingenious mechanical contrivance 
was invented by Griffiths, by which the blades 
were made to adjust their pitch to suit the resist- 


ance, the pitch of a blade being reduced when 
passing through the upper part of the circle, and 
increased when passing through the lower part. 
The apparatus would not stand much wear and 
tear. Unless a propeller has a good running 
balance it will tend to cause vibration. To insure 
steadiness when revolving at high speed, it is 
necessary that each blade should be of the same 
weight, and that the centre of gravity of each 
should be at the same distance from the axis of 
the shaft. 

There is a disadvantage connected with an in- 
clined screw-shaft, which has been generally over- 
looked. The result of depressing the end of a 
shaft is to cause the effective pitch to vary through 
every part of the revolution. If the inclination 
be supposed to be 45° for example, that part of the 
blade which is intended to have a pitch of three 
diameters, has, in reality, an effective pitch vary- 
ing from nothing to infinity. It is, of course, 
obvious that the pitch of the blades in relation to 
the axis is unchanged by any alteration in the 
direction of the shaft, but whatever the pitch in 
relation to the axis may be, if the axis were to pass 
vertically out through the bottom of the ship, the 
virtual or effective pitch, measured in the direction 
of motion, is nil. If a screw does not move along 
but has a motion of rotation only, the resistance of 
the water to the blades is the same whatever be 
the direction of the shaft, but if the propeller be 

D 2 



Fig. 17. 

allowed to move along while at the same time it 
be constrained to move horizontally, the shaft 
being inclined to the horizontal, then the resist- 
ance of the water to the blades is not uniform, but 
varies over every part of the revolution. This 
will perhaps be made clearer by an examination of 
the phases through which a blade passes during 
one revolution. It is convenient and suitable to 
consider the action of a screw as similar to that of 

an inclined plane moving 
past the stern. In Fig. 17 
the full line represents the 
upper blade as a plane 
moving from port to star- 
board, the dotted line repre- 
sents the lower blade as a 
plane moving from star- 
board to port. In Fig. 18 
the shaft is horizontal, and 
the full line shows the blade 
going down, and the dotted 
line the blade coming up. 
In Fig. 19 the shaft is in- 
clined at 45°, the full line 
again shows the blade going 
down, and the dotted line 
the blade coming up. Now 
as the ship moves forward 
the water flows to the sc^'ow in approximately 
horizontal lines, and the blade which at one part 

Fig. 18. 

Fio. VX 




of the revolution is edgewise to the water, at 
another is square on to it, and the result is a 
succession of shocks causing vibration. Another 
way of looking at it is this : — A particle of water 
meeting the ascending blade has its motion rela- 
tive to the vessel arrested completely, while a 
particle first meeting the forward edge of the 
descending blade would require to have its velo- 
city infinitely accelerated in a horizontal direction 
to enable it to escape from under the blade. This 
is what is meant by saying that in the above 
example the effective pitch varies from nothing to 
infinity during each revolution. 

The racing of screws is due to either of two 
causes. If the propeller breaks the surface of the 
water as the stern rises in a seaway, it will draw 
air down, and the resistance is immediately very 
much reduced. Referring to Plate 1, where the 
thrust is shown at different revolutions of a pro- 
peller, both when completely immersed and also 
when splashing, it will be seen that in the former 
condition a thrust of 11 lbs. is exerted at 680 
revolutions. When air is drawn down, the same 
thrust is exerted at 1000 revolutions, so that this 
propeller, if delivering a constant thrust, would 
vary its revolutions very rapidly from 680 to 1000 
if alternately raised and lowered as in the action of 
pitching. But it is not only when the screw breaks 
the surface that it will race. If a vessel is among 
waves, racing may occur, although the screw may 


not be emerged at all. Mr. Froude pointed out 
that this was probably due to the circular motion 
of the particles of water in waves. There is no 
real motion of translation in waves, the water 
which is travelling in one direction at the crest 
returns in the opposite direction in the trough. 
This circular motion extends to some distance 
below the surface, and a screw finds the resistance 
of the water augmented or reduced, as it is beneath 
the trough or crest of a wave, and reduces or 
increases its speed accordingly. 

A screw causes lateral motion of the stern of a 
vessel which has to be counteracted by the rudder. 
This efifect is very much greater when going astern 
than when going ahead, but the cause is not the 
same in the two cases. When going ahead Pro- 
fessor Osborne Reynolds has pointed out that the 
onward motion of the frictional wake is very 
different at the surface and at the keel. He agrees 
with Rankine that the mean speed of the wake in 
the case of a vessel of fairly fine form may be 
10 per cent, of the vessel's speed, but thinks it 
varies from 20 per cent, at the surface to nil at 
the keel ; the upper blade of the screw therefore 
experiences more resistance than the lower, and 
tends to drive the stern round. If the screw is 
right-handed, and does not draw air down, it will 
tend to cause the vessel to carry a starboard helm 
in order to maintain a course. If there is air in 
the wake, caused for example by the vessel being 


at a light draught of water, the effect is reversed, 
the lower blade predominates, and port helm must 
be carried. The natural effect of the screw may 
also be neutralised or even reversed if there is a 
broad counter over it and a large rudder, especially 
if, as is often the case, the part of the rudder 
behind the upper blade of the screw is larger in 
area than the part behind the lower blade. The 
reaction of the stream of water thrown from the 
upper blade upon the counter and upper portion 
of the rudder is greater than that of the stream 
thrown from the lower blade in the contrary 
direction upon the lower portion of the rudder, and 
may necessitate the carrying of a port helm with 
a right-handed propeller. Professor Eeynolds 
states that a right-handed screw without air 
always bears considerably on the port side of 
the stern-post, even when the ship carries a 
port helm, showing that the effect on the hull 
and rudder more than counterbalances the effect 
on • the screw. In the Engineer of October Ist, 
1886, was published a diagram showing the 
port and starboard strains upon a rudder as 
recorded automatically by Maginnis' "Rudder- 
graph." The screw was right-handed, and the 
diagram showed clearly that the ship required a 
starboard helm to keep a straight course. 

When the screw is reversed, and the vessel has 
gathered stern way, the propeller has a much 
greater influence upon the course of the ship than 


when going ahead. In the latter case the 
influence is always very small ; in the former it is 
often great. The engines will be observed to have 
a great tendency to race when going astern. The 
screw is then drawing air, and the upper blades 
suffer most, so that the lower blades experience the 
most resistance, and drive the stern round. A 
right-handed screw tends to move the stern to 
port, and a left-handed one to starboard. 

When a screw is suddenly reversed, and before 
the headway is off the vessel, the action of the 
rudder is not to be depended upon. The following 
is an extract from the report of the Committee 
appointed by the British Association to investigate 
the effect of propellers on the steering of vessels. 

British Association Report^ 1878. 

'< It is found an invariable rale that daring the interval in 
which a ship is stopping herself by the reversal of her screw, 
the rudder produces none of its usual efiToct to turn the ship, 
but that under those circumstances the efifect of the rudder, 
such as it is, is to turn the ship in an opposite direction from 
that in which she would turn if the screw were going ahead. 
The magnitude of this effect is always feeble, and is dififorent 
for different ships, and even for the same ship under different 
conditions of loading. It also appears that, owing to the feeble 
influence of the rudder over the ship during the interval in 
which she is stopping, she is then at the mercy of any other 
influences that may act upon her. Thus, the wind, which 
always exerts an influence to turn the stem of the ship into 
the wind, but which influence is usually well under control of 
the rudder, may, when the screw is reversed, become paramount, 
and cause the ship to turn in a direction the very opposite of 
that which is desired. 

" Also the reversed screw will exorcise an influence, which 


increases as the ship's way is diminished, to torn the ship to 
starboard or port, according as it is right or left-handed, this 
being particularly the case when the ship is in light draught. 
These several influences — the reversed effect of the rudder, the 
effect of the wind, and the action of the screw — will determine 
the course the ship takes during the interval of stopping. 

" They may balance, in which case the ship will go straight 
on, or any one^of the three may predominate." 

Notwithstanding that a screw has a tendency, as 
just described, to produce sideways motion of the 
stern, and so to cause a vessel to deviate from a 
straight course, it yet offers considerable resistance 
to lateral movement produced by external causes. 
The pressure on the blade which is moving in the 
same direction as that in which the stern of the 
vessel is turning is increased, while on the blade 
moving in the opposite direction the pressure is 
reduced, that is to say, if the screw is right-handed 
and the vessel is under port helm, the stem, conse- 
quently, travelling to port, the resistance of the 
lower blade which is moving towards the port side 
will be increased, and the resistance of the upper 
blade, which will be moving towards the starboard 
side, will be diminished, because the one is meeting 
the water, and the other is receding from it. The 
change of pressure will be proportional to the 
square of the angular velocity of the stern. The 
irregular pressure causes the vibration frequently 
noticed when a screw vessel is rapidly turning. 
This resistance to lateral motion is not without 
value, because if it is removed the condition of a 



Fig. 20. 

vessel moving in a straight line is one of instability'-. 
If the vessel makes the least angle to the direction 
in which she is moving, the excess of pressure due 
to undisturbed water at the bow tends to increase 
the divergence, and this tendency is resisted by 
the propeller. It seems probable that a vessel 
never maintains a line of advance in the exact 
direction of its axis, but always at a small angle 
with it. 

A very ingenious propeller has lately been 

patented by Mr, F. H. White, 
which, while retaining the 
advantage of rigid blades 
in resisting lateral motion 
when a vessel is on a straight 
course, is so arranged that 
the blades are under control 
and can be feathered in such 
a way as to cause them not 
only to offer no resistance 
to turning, but to actively 
assist in it. It is in fact a 
steering propeller of a very 
simple description. It is 
illustrated in Figs. 20, 21, 22. 
The screw-shaft terminates 
in a universal joint which 
connects it with an exten- 
sion of itself in the form of a smaller shaft or 
tail-piece. The joint can be made in several 


foi-rae, but the simplest is shown in Fig. 20 
where the centre or connecting piece has four 
arms at right angles to each other. The blades 
are rigidly fixed to tlie two arms which are di- 

rectly held by the jaws of the main shaft. See 
Fig. 20, which ebows the screw in elevation. 
Any movement of the tail-piece causes an altera- 
tion in the pitch of the blades, an increase in the 
pitch of one blade being accompanied by an equal 



decrease in the pitch of the other. The eflfect of 
the change of pitch is that the stem of the vessel 
is forced either in one direction or the other, 

Fig. 22. 

according to which side the tail-piece is moved. 
When it is desired to change the course of the 
vessel to the right, the tail-piece is moved to the 
right, its manipulation being thus similar to that 



of the rudder to which it may be attached as 
shown in Figs. 21 or 22, The joint is covered 
with a light casing as shown in Fig. 21. The 
screw may have two, three, or four blades. A 
characteristic which adds much to the practical 
value of the design, is that the feathering of the 
blades is greatly assisted by the action of the 
water-flow itself, as any alteration in the course 
of the vessel tends to change the pitch of the 
blades in such a manner as to bring the tail- 
piece into that position which would of itself cause 
such an alteration, so that after having initiated 
the feathering motion, it may be anticipated that 
the tail-piece will have little more to do than to 
control and regulate it. 

When auxiliary steam power has to be applied 
to sailing vessels, it is best, if possible, to arrange 
the screw so that it can be lifted out of the water. 
If disconnected and allowed to revolve it causes 
considerable resistance. If it cannot conveniently 
be lifted, it is advisable to use a screw with two 
narrow blades, which can be set up and down in 
a line with the stern-post, and feathered fore and 
aft by internal mechanism as arranged by Bevis. 
With a view of reducing the drag under sail to a 
minimum, Messrs. Thornycroft tried a propeller 
with flat blades, which could be feathered in line 
with the shaft for sailing, and set at an angle 
with it for steaming, but it was found to be a very 
inefficient propeller, requiring just double the 



horse-power for a given speed as was needed for 
an ordinary screw. Fig. 23 shows the results 
obtained with it, compared with those given by 
an ordinary screw by which it was afterwards 

FiQ. 23. 












IMP. ^^ 









300 ^ 



- 200 


II ilE I& 

Speod in knots. 
Compai:atiTe trial with common and with flat-bladed propellers. 

Vessels intended for towing require large screws, 
because, if the screws are designed to work at their 
best efficiency against the small resistance of the 
tug alone, the slip when towing will be excessive, 
and will cause an undue wast^ of power. It is 
desirable to so design the propeller that it shall 
give a maximum return at the speed which the 


tug may be expected to attain when towing an 
average load. 

' Screws for electric launches labour under the 
disadvantage of having to run at an exceptionally 
high speed of revolution. The blades should be 
very thin and sharp, and two blades will give less 
resistance to turning with a given surface than 
three. It is difficult to estimate the pitch necessary 
to give a required number of revolutions, because 
it is a peculiarity of the motor, that the slower the 
rate at which the screw turns, the faster the power 
is run down, and vice versd. It may be compared 
in this respect to the steam siren which uses a large 
amount of steam when revolving slowly, and the 
more rapid the rate of turning the less is the 
quantity of steam passed. 

The fastest running screws of which the author 
has had experience were made by Messrs. Thorny- 
croft, for the Howell torpedo. They are 6 inches 
in diameter, and run at 5000 revolutions per 
minute, driving the torpedo at 30 knots. 

Twin screws possess very many advantages over 
a single screw, and are quite as efficient. In very 
fine ships the length of the outside shafting 
becomes a serious consideration, and the necessary 
supports add to the resistance. In order to reduce 
this inconvenience to a minimum, the well-known 
firm of Rankin and Blackmore introduced an 
arrangement of twin screws with overlapping discs 
in the 'tug Otter, built in 1876, One propeller 



was set in front of the other, the. blade-tips passing 
through an aperture in the dead wood. Figs, 24 
and 25 show twin screws as fitted in the Buzzard^ 
a small coasting steamer belonging to Mr. John 
Burns. The arrangement has proved successful, 

Fig. 24. 

and has been frequently adopted, the most notable 
examples being the s.s. Teutonic and Majesticy built 
by Messrs. Harland and Wolff. The screws of the 
Teutonic are 19 feet 6 inches in diameter, and the 
distance between the shafts is IG feet. One screw 
is 6 feet 3 inches behind the other. They are right 
and left-handed, and turn outwards. In a twin 
screw torpedo boat built by M. Normand, with 
overlapping screws, both are arranged to turn the 
same way. The overlapping blades thus cross one 
another, and the water thrown up by the ascending 


blade of one screw is met by tlie descending blade 
of the other, and the slip is reduced. It is found 
tbat when so arranged, the aftermost propeller 
turns slower than the foremost one, the contrary 
being of course the ease when they turn in opposite 

Fio. 25. 

Triple screws have not as yet been widely 
introduced. An interesting series of comparative 
trials with twin and triple screws was made by 
M. Marcbal at Lorient, and described by him in a 
paper read at the Institution of Naval Architects 
in 1886. His summing up of the results is that 
" three screws are, from the point of view of speed, 
very nearly equivalent to two screws of the same 
propulsive surface and immersed to the " same 


depth, when the most favourable position is chosen 
for each system." * Recent examples of the 
application of three screws are the French armoured 
cruiser Dupuy de Ldine^ and the United States 
cruiser known as No. 12, of 21 knots speed and 
20,000 I.H.P., and some Italian torpedo cruisers 
engined by Messrs. Hawthorn, Leslie, & Co. 

There would appear to be several advantages to 
be anticipated from the adoption of triple screws 
in high-speed ships of war. It is possible by this 
means to effect a reduction in weight of machinery 
since a higher speed of revolution is admissible. 
There would probably be a saving of fuel when 
cruising at slow speeds by using the centre screw 
alone. In twin screw ships of small beam in pro- 
portion to length, it is more economical to use one 
propeller only at slow speeds, and to disconnect 
the other, as the drag of the idle screw and of the 
small angle of helm required to maintain a course, 
are more than compensated for by the reduction 
of engine friction and the superior economy of 
steam obtained by working one engine at a greater 
proportion of its maximum power, and a still 
further economy might be expected from the 
increased subdivision of engine power in triple 
screw ships. 

* TranSi Inst. Naval Arcbitects, xxyii. p. 239. 

( 51 ) 



For a screw of any given pitch-ratio, there is 
a particular slip - ratio corresponding to its 
maximum efficiency. A greater or less amount of 
slip than this will result in a smaller return of 
useful work in proportion to the power expended 
in driving the screw. By slip-ratio is meant the 
ratio P R to V, where 

P = mean pitch ; 
R = revolutions ; 

V = velocity of feed, or speed of screw through 
the water. 

The best way of determining the slip -ratio 
which is suitable for any given ratio of pitch to 
diameter is by experimenting upon a series of 
model screws of some selected type, each diifering 
only in the ratio of pitch to diameter, and the 
following conditions maybe laid down as essential, 
if the results obtained are to be useful for general 
application : — 

1. Each model must be tried at a number of 
different slip-ratios. 

E 2 


2. The velocity of feed must be capable of 
accurate measurement. 

3, The power expended in driving the screw 
must be measured, and it must be the power put 
into the screw-shaft, and not complicated with 
engine friction, which is an unknown quantity. 

It is clear, therefore, that no experiments would 
be satisfactory, in which the screw under examina- 
tion was working in the wake of a vessel, because 
it would then be impossible to measure the velocity 
of feed, since the forward motion of the wake is an 
unknown quantity, and varies with the speed of 
the ship in an unknown manner. 

The late Mr. W. Froude, by means of an ideal 
conception of a small element of helical surface, 
rotating at the end of a non-resisting radial arm, 
deduced by theory for the screw, results very similar 
to those which were afterwards yielded by experi- 
ment.* In 1877, Mr. Froude described how such 
experiments were being conducted at Torquay ,f 
and a very full account of the system pursued, not 
only for ascertaining the screw efficiency, but also 
for investigating the effect upon the operation of 
the screw of the presence in front of it of the hull 
of the ship, was given by Mr. R. E. Froude in 
18 83. J All these papers should be consulted by 
any one proposing to experiment for themselves. 

* Trans. Inst. Naval Architects, xix. p. 47. 

t Proc. Inst. Civil Engineers, li. p. 38. 

\ Trans. Inst. Naval Architects, xxiv. p. 281. 


In the years 1879-80, Mr, John I. Thornycroft 
made a number of experiments with models of 
small dimensions, and a detailed description of 
these will be given as they are interesting as 
showing what can be done with moderately simple 

The models were about 9 inches in diameter, 
and this size was found to be convenient. The 
maximum thrusts did not exceed 30 lbs., so that 
although the scale was large enough to admit 
of accurate measurement, a moderately small 
dynamometric apparatus could be employed. They 
were made as follows : — A wooden block was pre- 
pared from the reduced propeller drawing, upon 
which a blade was modelled by hand in paraffin. 
A mould of the blade was made in plaster of paris, 
into which was run an alloy consisting of tin and 
bismuth, the latter in small proportions. This 
material is sufficiently soft to be scraped and cut 
with a knife, and at the same time is strong enough 
to retain its form. It, of course, does not rust. 
The cast blade was then filed, burnished, and 
accurately fitted to the wooden block if it had 
become at all distorted. The blades were secured 
in the boss by screws in such a way that the pitch 
could be varied to any desired extent. A steam 
launch was fitted up with a small shaft passing 
through the bow to carry the model screw, the 
shaft projecting a sufficient distance in front of the 
launch to ensure that the model should work in 


undisturbed water. This shaft could move very 
freely in its bearings to and fro, and the end of it 
was attached by means of a steel pianoforte wire 
to a spring, so that the thrust exerted by the pro-, 
peller could be recorded. This shaft was made to 
revolve by means of a gutband working on to a 
pulley, and driven by means of a small engine of 
one or two horsepower. The measurements made 
were : — 

1. The thrust exerted by the model. 

2. The revolutions of the model. 

3. The speed of the launch. 

4. The turning effort expended in driving the 

5. Equal intervals of time. 

The constant friction of the engine and shafting 
was also measured in order to get the true zero for 
the turning effort diagram. A dynamometer was 
constructed, by which records were continuously 
made upon a revolving drum driven at a uniform 
speed by means of clockwork. A number of pens 
over the drum were each connected to an electro- 
magnet in such a way, that so long as no current 
flowed the pens were stationary, and traced straight 
lines upon the paper as it revolved beneath them. 
When contact was made the pens were jerked and 
made a lateral indent in the line. One pen was 
electrically connected with a clock, and measured 
intervals of time, making an indent every 12 
seconds. A second pen recorded the revolutions 


of the main engine driving the Jauneh, these 
revolutions aiFording a means of checking the 
speed. A third pen recorded the revolutions of 
the model, a counter on the shaft making contact 
every 50 revolutions. The speed of the launch 
was found by passing a fixed distance on shore 
of 300 feet, the time of passing the posts being 
marked by an electric pen actuated by the observer 
pressing a button. As the observations were taken 
in a tideway two runs were necessary to determine 
the speed for every observation, one upstream 
and one down. Another pen was connected to a 
spring before mentioned, to which the model shaft 
was attached, and recorded the extension of the 
spring and thrust of the propeller. The last pen 
showed the tension of the gut driving the model, 
and thus measured the turning eflfort upon the 
shaft. This tension was obtained by the arrange- 
ment shown in Fig. 26. The large pulley in the 
centre is driven by the small engine of which the 
cylinder, piston-rod, connecting rod, and crank-arm 
are indicated in the figure. The lower pulley is 
on the shaft of the model propeller. The two 
upper pulleys are carried by a bar pivoted at the 
centre. Rigidly attached at right angles to this 
bar is a long lever, the weight of which is balanced 
by the ball at the top. The motion of the lever is 
limited to a short travel on each side of the vertical 
by stops not shown in the figure. A spring is 
attached to the bottom of the lever, and its exten- 


sion is automatically recorded upon the diagram. 
The driving band is passed round the pulleys as 
shown, the direction of its motion being indicated 
by arrows. When the central pulley is made to 

revolve, the tension of the gut pulls down the left- 
hand pulley, and extends the spring until its 
tension is sufficient to prevent further motion of 
the lever. An adjustment is provided in the cord 
between the spring and the lever, eo that the latter 
may be maintained approximately vertical. 

If Ta is the tension of the ascending or tight 
side of the hand, T, the tension of the descending 


or slack side, and P the pull in pounds as measured 
by the spring, then 

and turning moment = (Tj — Ti) x 2 ir r x revo- 
lutions of r per minute. 

The launch, which as before stated was driven 
by an independent screw, maintained an approxi- 
mately constant speed of about 4^ knots, and a 
number of observations were taken at different revo- 
lutions of the model and plotted as shown in Plate 1. 
Curve A is the thrust of the model, B is the useful 
work in foot-pounds per minute, being the product 
of the thrust into the speed through the water. 
C is the work expended in foot-pounds per minute. 
The useful work divided by the work expended is 
a measure of the efficiency of the model as shown 
by curve D. 

A convenient way of utilising the results thus 
obtained is to construct a series of constants, which 
will express the relation between disc-area, power, 
and speed, at different slip-ratios. A second series 
of constants can be formed expressing the relation 
between diameter, speed, and revolutions. These 
constants depend upon the following laws : — 

1. For a given pitch-ratio and efficiency the 
disc-area is proportional to the horse-power, and 
inversely proportional to the cube of the speed. 

2. For a given pitch-ratio and efficiency the 
revolutions per minute are proportional to the 


speed, and inversely proportional to the diameter. 
They might take the following forms : — 

01 = disc-area in square feet x 


Cb = revolutions per minute x — • 


Where i; = velocity of feed ; 

H.P. = effective horsepower in the screw-shaft. 

In this shape, however, it would only be possible 
to obtain from them directly the proportions 
proper for a screw to propel a " phantom ship " — 
that is a ship which would require the same thrust 
to propel it at any given speed as a real ship, but 
which will create no disturbance in the water, 
driven by a " phantom engine "—that is an engine 
without friction. In order to make them available 
for general use, it is more convenient to substitute 
V = speed of ship for v = velocity of feed, and 
I.H.P. for effective horsepower in the shaft. In 
order to do this it is necessary to make certain 
assumptions as to the speed of the following 

E H P 

current and as to the ratio ' ' ' and as these 


will vary with the form of the ship and with the 
type of engine respectively, an element of un- 
certainty is here met with, and much will depend 
upon the judgment of the designer, as to whether 
it is necessary to apply a wake correction or a 
propulsive coefficient correction, or whether the 
standard values assumed for these factors may be 
supposed to be a sufficiently close approximation. 


The standard wake has been taken as 10 per 
cent, of the speed of the vessel. In a very full 
ship it might be as much as 30 per cent. There- 
fore V the speed of the ship should be reduced, 
when using the constants, by 20 per cent, for a 
very full ship, and by amounts varying from 
20 per cent, to nil, as the fulness of form varies 
from *' very full " down to what may be considered 
a " fairly fine " vessel when no correction need be 

Table II. p. 74 gives the value of the wake cor- 
rections for a few vessels. The standard ratio of 

' ' ' has been taken as "5. A correction can 

be made for any deviation from this assumed value. 

If, for example, the E.H.P. is estimated at 55 per 

cent, of the I.H.P,, the I.H.P. must be multipliM 

by the ratio j^tt . 
•^ 50 

Again, the constants are primarily correct for 

four-bladed screws; they can be used for three- 

bladed or two-bladed screws by multiplying the 

I.H.P. by ^78(55 or ^Tgg respectively. 

The form, therefore, which the constants finally 
take is 


Oa = disc-area in square feet X jWp- > 


Or = revolutions per minute X ^ • 

Where V = speed of ship in knots. 


If constants are constructed in this way from 
the curves in Plate 1 corresponding to different 
amounts of slip, a row of figures is obtained, such 
as is shown by any one of the horizontal lines in 
Table I., p. 73, and these can be placed in their 
proper relative position under a curve of efficiency. 
For example, to find the constants C^ and Cr 
corresponding to 750 revolutions of a three- 
bladed model from the curves in Plate 1 : — 

Diameter of model = 9 inches. 

. * . Disc-area = * 441 sq. feet. 

Work expended in foot-poonds = 9625. 

Useful work ^ 6330 ^ ^^g ^ ^velocity of feed in feet 
Thrust in pounds 14-8 \ per minute. 

^ = 4-22 knots. 

•441 X f4-22 X 4y 

Ca = ^i '^ = 90. 

•683 X -865 

Ch= ^^^^'^^ = 120. 
4-22 X .-i 

The object Mr. Thornycroft had in view in 
making the experiments was to test the efficiency 
of the screw-turbine propeller as compared with 
the screw he was then using on torpedo boats,* 
and he therefore did not carry out a complete set 

* See a paper by Mr. Thornycroft in Trans. Inst. Naval 
Architects, xxiy. p. 42. 


of experiments upon a common screw, which 
would have involved a series of trials with a 
number of models of varying pitch-ratio, but 
contented himself with ascertaining that a small 
change of pitch on either side of that for which 
the propeller was cast, obtained by twisting the 
blades in the boss, did not increase the efficiency, 
but rather reduced it. 

This complete series was, however, afterwards 
carried out by Mr. R. E. Fronde at Torquay, and 
the results were given by him in a paper read 
before the Institution of Naval Architects in 1886.* 
They corroborated generally those obtained at 
Chiswick, except in one particular. So far as 
could be judged by Mr. Froude, there was scarcely 
any diflFerence in maximum efficiency within such 
a large range of pitch-ratio as from 1 • 2 to 2*2. 
As almost precisely the same maximum was 
obtained by Mr. Thornycroft with a pitch-ratio 
of 1 • 14, it seems reasonable to suppose that these 
even may hardly be considered as hard and fast 
lines beyond which efficiency will decline, and 
Mr. Froude considers that they may be fairly 
extended to • 8 on the one side and 2 • 5 on the 

It must, however, be borne in mind that 
this equality of efficiency is manifested by screws 
working in open water. There is a very general 
consensus of opinion that small pitch-ratios give 

* Trans. Inst. Naval Architects, xxvii. p. 260. 


the most favourable results in practice. If this 
opinion is justified, the explanation must be that 
large pitch-ratios cause a greater augmentation of 
hull resistance. That this would be so might be 
inferred from the reasoning on p. 21, which leads 
to the conclusion that such screws produce a 
greater suction than those of fine pitch. Although 
accepting the parity of efficiency of different pitch- 
ratios within the limits experimented upon, when 
the screws are considered apart from the vessels 
they propel, the author thinks that there is reason 
to suppose that there will be a loss involved in the 
use of a screw of coarse pitch, if it is placed in 
such a position that the increased suction produced 
by it is able to take effect upon the hull of the 

Mr. Froude also found a great similarity between 
the curves of efficiency at different pitch-ratios, 
the only apparent effect of change of pitch-ratio 
being to cause the maximum efficiency to occur at 
different slip-ratios. Where, for example, the 
efficiency of one propeller reached a maximum at 
15 per cent, slip, the efficiency of another of 
different pitch-ratio was at a maximum at 20 per 
cent, slip, and so on. It was therefore possible to 
superimpose the curves and cause them to coincide 
by the simple device of empirically changing the 
scale of slip-ratio. Mr. Froude very kindly gave 
the author permission to give the results of the 
Torquay experiments in a paper for the Institution 


of Civil Engineers on '* The Screw Propeller,* for 
which purpose the author compiled Table I., 
p. 73, in which each horizontal line of figures 
corresponds to a particular pitch-ratio and contains 
constants for disc-area, and revolutions at diflFer- 
ent amounts of slip as calculated from a set of 
curves such as that shown in Plate 1, and in 
the manner already described. These all occupy 
their proper relative positions under the curve of 

The table embraces the whole of the experi- 
ments possible with a particular type of screw, 
including pitch-ratios extending from 0*8 to 2*5, 
and slip-ratios from the lowest to the highest 
which is considered practicable. 

It would be used in the following manner: — 
Let it be supposed, for example, that the size of 
the screw is limited by the draught of water. If 
the given disc-area is multiplied by the cube of the 
speed of the vessel in knots and divided by the 
I.H.P., the constant C^ is obtained. Suppose it is 
360. The nearest figure to this in the column under 
the maximum efficiency should be sought, and its 
position, when found, indicates the pitch-ratio 1*6, 
which will be in the same line at the left hand of 
the table. Adjoining the disc-area constant 360 
will be found the revolutions constant 71. This 
number, multiplied by the speed of the vessel in 
knots, and divided by the diameter of the screw in 

* Proc. Inst. Civil Engineers, cii. p. 74. 


feet, will give the number of revolutions at which 
a four-bladed screw should run to obtain the 
maximum efficiency. 

It is evidently desirable to select the constants 
from the column under the maximum efficiency, 
but in special cases when the revolutions are 
required to be either exceptionally high or excep- 
tionally low in order to suit existing engines, the 
same disc-area constant may be taken from one of 
the other columns where it will be found associated 
with either a lower or a higher value of Or accord- 
ingly as the slip ratio is greater or less ; and it is 
possible to see at a glance what sacrifice it is 
necessary to make in efficiency in order to obtain 
the required result. 

If the product of the Or constant multiplied by 
its proper pitch-ratio is greater than 101 • 33 the 
apparent slip will be positive; if less, it will be 
negative. The amount of the slip in either case 
will be given by 

Qxv * P^M - 101-33 ^ irtrt 
Slip per cent = *- — i- — x 100 ; 

where j9 = pitch-ratio. 

The same constants are presented in a graphic 
form in Plate 2, in which each vertical column of 
Table I. is plotted as a curve and values of C^ 
and Or corresponding to intermediate pitch-ratios 
may be thus obtained. 

The method of correcting for two and three 
blades and also for different values of wake is 


due to Mr. R. E. Froude, and Table II. was given by 
him for the purpose of fixing upon a suitable wake 
correction in his masterly paper already referred 
to,* which is worthy of the most careful study. 
Mr. Fronde's screws were of uniform, pitch, and 
the blades were elliptical. The width in the 

middle of the developed blade was • 4 ~. 

It follows that the developed surface, supposing 
each blade to be a complete ellipse, would be 

For a four-bladed scrow = disc-area X * 4 
„ three „ = „ x 0*3 

„ two „ = „ X 0-2 

As the developed area is usually taken as ex- 
clusive of the boss, the portions of the ellipses cut 
oif by it must be deducted. A few examples of 
the use of the tables will be given at the end of 
the chapter. 

It will be noticed that the disc-area constants in 
the columns under maximum efficiency permit great 
latitude in the choice of diameter for a given 
I.H.P. and speed, so that if consideration is con- 
fined to the screws alone apart from the vessels 
they are designed to propel and the service these 
vessels are intended to perform, within these 
limits the efficiency is independent of the actual 
size. For example, take the case of a vessel of 

* Trans. Inst. NaVal Architects, zxyii. p. 250. 



good form having engines of 500 I.H.P. and 
expected to attain a speed of 10 knots. From 
Table I. equal efficiency may be expected with a 
screw having a diameter of 10 feet and 0*8 pitch- 
ratio, and with one having a diameter of 15^ feet 
and a pitch-ratio of 2 • 5. The first would run at 
138 revolutions per minute, the second at 33^. 
Some remarks have already been made (see p. 61) 
touching the eflFect of pitch-ratio upon efficiency, 
but in considering the relative advantages of large 
and small screws the duties required of the vessel 
must be taken into account. Suppose it is desired, 
for example, to maintain a high speed against 
head winds and seas. It is generally sup- 
posed that a large screw or a large surface is 
all that is required, but if we consider what 
happens when a vessel meets head winds we shall 
see that this is not necessarily so. In such circum- 
stances the speed of the ship is checked, the revo- 
lutions of the screw remaining practically un- 
affected, so that the slip-ratio is increased. If this 
is already sufficient to give maximum efficiency 
at the smooth water speed, the efficiency will be 
reduced when the slip is increased by the wind, 
and it is probable that the 15^foot screw of 2' 5 
pitch-ratio would waste as much power as the 
10-foot screw of • 8 pitch-ratio, although one has 
nearly 2^ times the surface of the other, because 
they both have the same position to start with as 
regards the curve of efficiency. Large diameter 


associated with large pitch-ratio is valueless for 
the purpose ; what is required is that the slip-ratio 
shall not be excessive when the speed of the vessel 
is retarded by external resistances. The case is 
analogous to that of a tug, and must be similarly 
treated- The best proportions will be obtained by 
designing for a speed less than the maximum 
smooth-water speed, but such as the vessel is ex- 
pected to maintain over an average passage. The 
propeller would have a somewhat reduced efficiency 
when the vessel was developing her full power 
over the measured mile, would in fact be too large, 
but would work at its best at the speed assumed as 
the average, and should effect a saving of fuel on 
the voyage. When the diameter is limited the 
blade-surface may be increased with advan- 

It has been stated by Mr. Hall-Brown * that for 
vessels of very full form — a class with which he 
has had much experience — a large diameter and a 
small pitch-ratio are essential to success, and he 
attributes the necessity to the influence of dead 
water as distinguished from frictional wake (see 
p. 33). In such a case the blades must reach well 
out into water clear of the stern, so that the pro- 
portion of dead water to the total area of stream 
acted upon may be as small as possible. Mr. Hall- 
Brown gives the particulars of what is found to 

* Proc. Inst Civil EngineorB, cii. p. 131, 

F 2 


be a good screw for a cargo vessel of the following 
dimensions :— 

Length B.P 277 feet 

Beam (moaldod) 37*5 „ 

Draught 19 feet 11 inches 

Displacement •• 4670 tons 

Block coefficient -792 

LH.P 825 

Speed 9 knots 

Diameter of screw 16 feet 

Pitch „ 16 „ 

Reyolations 64 

The values of C^ and Cr are 184 and 115 re- 
spectively, which agree with the constants in the 
table for 1*0 pitch-ratio at 69 per cent, efficiency, 
but as the table is calculated for a wake value of 
10 per cent., corresponding to a fine form of 
vessel, he suggests that this points to the conclu- 
sion that the propulsive coefficient is very low on 
account of the action of the screw upon the dead 
water, and that the two corrections for wake and 
propulsive coefficient tend to annul one another. 
In such a case it might be expected that a better 
performance would be obtained if twin screws 
were employed, as these would be to a great 
extent clear of the dead water. 

Whenever the ship is of exceptional form, no 
exact rules can be given for the proportions of 
screws deduced from model trials in undisturbed 
water. Certainty can only be obtained by trying 
the model screw behind a model of the ship, and 
this is always done by Mr. Fronde in the case of 


new Admiralty designs. But every carefully 
recorded ship trial is in one sense a model experi- 
ment of this character, and when a screw is to be 
designed for a ship of a special type, it is safer to 
calculate the values of C^ and C„ from the actual 
figures obtained from the trials of some vessel, of 
proportions as similar as possible, which has given 
a good result, because the values of wake and 
propulsive coefficient may then be assumed to be 
similar also. In place of constructing constants, 
the following more direct method may be 
employed : — 

To find the diameter of a propeller for a 
given I.H.P. and a given speed from the diame- 
ter of another similar propeller at a different 
I.H.P. and a different speed. 

If c2 =r diameter of model, which may be larger or smaller 
than D ; 
D = diameter of required propeller ; 
p = I.H.P. of model ; 
P = I.H.P. of required propeller ; 
V = speed of vessel with model propeller ; 
V = „ „ required „ 

r = revolutions of model propeller ; 
R = „ required „ 



/ v^ P 

R = r X - X 1- 

V D 

The pitch-ratio must be the same as that of the 
screw which is treated as the model. 


Examples in the use of Tables /. and IL 

Example 1. — Find the diameter and revolutions 
of a screw to work at maximum efficiency for a 
vcsstJ of 20 knots speed and 6000 I.H.P. Pitch- 
ratio to be 1 • 2. 

The disc-area constant (Ca) in the table for this pitch-ratio 
is 288. 

The revolutions constant (Ck) in the table for this pitch-ratio 
is 92. 

Disc-area = C^ X ,c ?'^'f' , vs = 288 x-?^^=2168<i. ft. 

(Speed m knots)* 2(y* * 

.*. Diameter = lG*5feet. 

T> 1 X- i-i speed in knots ^^ 20 ^ ^ , 

Eevolation8= Cr x -j^ — - — ^7—- = 92 x tt-t = HI- 

diameter m leet 16*5 

Example 2. — Find the pitch and revolutions of 
a screw to work at maximum efficiency for a vessel 
of 20 knots speed and 6000 I.H.P. Diameter not 
to exceed 15*5 feet. 

Disc-area =189 square feet. 


Ca = 189 X 777:7:7: = 252. 

Neaiest disc-area constant in table under maxi- 
iijum efficiency is 251 at pitch-ratio 1*0. 

. • . Pitch = 15-5 feet. 

The corresponding value of C, is 109. 

. • . Revolutions = 109 X -rz-z, = 141. 


Example 3. — Find the pitch-ratio and efficiency 
of a screw for a vessel of 20 knots speed and 6000 


l.H.P. The diameter to be 15 '5 feet and the 
revolutions about 80 per minute. 

Disc-area = 189 feet. 

^^ = ^^^ ^ 6000 = 2^2- 
Cb = 80 X 1^^^ = 62. 

The nearest constants in table are at pitch-ratio 
2'2 and efficiency 68 per cent. Where the 
diameter and revolutions are both limited, the 
curves on Plate 3 will probably be found more 
convenient, as intermediate pitch-ratios can be 

Example 4. — Find the diameter and pitch of a 
screw to work at maximum efficiency for a vessel 
of 20 knots speed and 6000 l.H.P. Revolutions to 
be 85. Wake correction to be made for a form of 
the fulness of H.M.S. Devastation^ corresponding 
to a wake percentage of 15 • 8. 

The multiplier from Table II. is 0-942. 

20 X 0-942 = 18-8 knots. 

By trial and error it will be readily found that 
the constants 306 and 85 for disc-area and revo- 
lutions respectively, at 1*3 pitch-ratio, will give 
the required number of revolutions, thus : — 

306 X 77rt-i^ = 276 square feet. . • . D = 18-75 feet 
(18 •8)' 


85 X - ,, „^ = 85 revolutions nearly. 
18-75 '' 


Example 5. — Find the diameter, pitch, and 
revolutions of a three-bladed screw to work at 
maximum efficiency for a vessel of 20 knots speed 
and 6000 I.H.P. Pitch-ratio to be 1 • 2. 

C^ = 288. Cb = 92. 
6000 LH.P. X ^-^ = 6940. 

288 X ^^ = 260 square feet . • . D xs 17-8 feet. 

92 X j|?3 = 103 revolutions. 
Pitch =(7-8 X 1-2 = 21-3 foot 









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of its axis, it will trace a curve known as the 
helix. Imagine the cylinder cut on one side by a 
straight line parallel to the axis meeting the helix 
in consecutive points A C (Fig. 27), and then 
imroUed and laid flat, the circumference through 
A will become the straight line A B ; B C at 
right-angles to it will represent the direction of the 
axis while that part of the helix formed during a 
complete revolution of the tracing point will be 
represented by the line A C. Since the distances 
moved by the point in the directions A B, B C are 
proportional, A C is a straight line. B C being 
the distance moved through in the direction of the 
axis, while the point goes once entirely round the 
cylinder, is the pitch, while the angle BAG, which 
the unrolled helix makes with a plane at right- 
angles to the axis, is the angle of tlie helix or 

If a straight line move uniformly round an axis 
which it intersects, and to which it is always at 



right angles, advancing at the same time uniformly 
in the direction of the axis, it will sweep out a 
surface known as a helicoid, and every point in 
the generating line will trace a helix as described 

FiQ. 27. 

above, necessarily lying on this helicoid. Since, 
during a complete revolution of the generating 
line every point moves through the same distance 
in the direction of the axis, the helicoid is a surface 
of uniform pitch, that is B C, Fig. 27, is constant 
for the helices traced by all points in the generating 
line. A helicoid can therefore be, and often is, 
used for the acting face of a screw-blade of uniform 
pitch. It is not necessary, however, that the gene- 
rating line should be at right angles to the axis ; 
such a surface may be generated by any line, 
straight or curved, moving uniformly along and 
revolving uniformly around an axis, intersecting 
and always making the same angle with it. 

The helix traced by any point in the gene- 


rating line will also be the curve of intersection 
with the screw surface of a co-axial cylinder of 
radius equal to the perpendicular distance of 
the point from the axis. The larger the radius 
of the cylinder, the larger of course the length 
of the circumference, as A' B, Fig. 27, and as 
the pitch is constant, it follows that the angla 
of the helix must ^^^t'^^a^^ Qfl ^^^^ radius of th( 
inters ectinpj' cylinder innrftimpig. We thus arrive 
at the fundamental geometrical property of a 
surface of uniform pitch, viz. : — Co-axial cylin- 
ders intersect it in helices, all of which have the 
same pitch, but whose angles vary, decreasing 
as the radius of the cylinder increases. Near 
the axis, therefore, the helices will approximate 
in direction to that of the axis, and as the dis- 
tance from the axis increases, they will lie more 
and more at right angles to it. If 6 be the angle 
of the helix, p the pitch, and r the radius of the 


intersecting cylinder, tan = « • 

The curve of intersection of a co-axial cylinder 
with a screw surface will hereafter be referred to 
briefly as the ** curve of intersection," or the 
"helix of intersection." 

In commencing the design of a propeller for a 
given ship, the diameter and pitch must be first 
decided, and the considerations which will deter- 
mine these having been fully dealt with in the 
preceding chapter it is only necessary to say that 


it is usual to provide for an immersion of the tip 
of the upper blade equal to about y^^ the diameter 
of the propeller, and to allow a clearance from 
the ship's side varying from 6 inches in small 
ships to 1 foot in large ones. 

With regard to the number of blades to be used, 
if the necessary disc-area can be obtained with a 
three-bladed propeller it is to be preferred, but 
if the draught of water is limited, a four-bladed 
propeller is practically equivalent to a three-bladed 
one of rather larger diameter. 

The expanded blade-area of the Admiralty 
standard blade is an ellipse of major axis equal 
to the radius of the propeller, and of minor axis 
equal to -^^ the major axis. It is often found, 
however, that owing to the diameter being limited, 
sufficient blade-area is not obtainable by these 
proportions; in such cases the elliptical form is 
adhered to with an increased minor axis of from 
•5 to '55 the major. 

If sufficient area cannot thus be obtained even 

with four blades, as in the case of shallow draught 

vessels where the diameter is very limited, the 

elliptical form may be greatly departed from, and 

the blade widened at the tip. A boss of diameter 

- diameter of propeller .„ _ 

equal to gi fQ 3 1 w^H cut away about 

^ the area of the standard ellipse. 

The expanded blade-area, which may be de- 
scribed as a flat surface of approximately equiva- 


lent area to that of the blades, both as to amount 
and disposition, is derived as follows : — 

A co-axial cylinder will intersect the screw 
surface in a helical curve making a certain angle 
with the axis, and it will intersect a plane passing 
through that diameter of the cylinder which passes 
through the middle point of the helical curve, and 
making the same angle with the axis in an elliptical 
arc. The length of the screw being small com- 
pared with the pitch, these two arcs will nearly 
coincide, and no great error will be involved by 
assuming that they do coincide. Imagine these 
elliptical arcs at all radii to be swung round a 
common centre line till they all lie in the same 
plane with their major and minor axes respectively 
coincident (though necessarily of diflFerent length), 
then the curve passing through their extremities 
will form the boundary of the expanded blade- 
area. This area is very nearly equal to the actual 
whole surface of the acting face of the blade, being 
in fact, somewhat less than it. 

To draw a right-handed uniform pitch screw of 
Admiralty or Griffiths type, with elliptical blades 
of standard form, with generating line at right 
angles to the axis, with axis horizontal and centre 
line of blade upright : — 

Draw a straight line A B, Fig. 28, Plate 3, to 
represent the axis of the propeller, and B C at 
right angles to it equal to the radius of the pro- 
peller. With B C as major axis and minor axis 


equal to -j^ of B 0, describe the ellipse B D E. 
Draw the circle F H G of radius equal to that ot 
the boss, cutting the ellipse in FQ-, the area 
GDCEFHG is the expanded area. Divide 
H into a number of parts, preferably equals at 
the points a, 6, c, rf, e, /. If p be the constant 

pitch of the propeller, take B A equal to -^ and 

join A H, Aa, A6, Ac, &c., these lines are called 
the pitch-lines. Then since the tangent of the 
angle which any one of these lines passing through 
a point on B C distant r from B, makes with B is 

o , these angles are the angles of the corre- 
sponding helices of intersection, and, therefore, by 
the assumption previously explained, they are the 
angles which the planes of the elliptical arcs form- 
ing the expanded area make with the plane at 
right angles to the axis of the propeller when the 
arcs approximately coincide with the correspond- 
ing helices on the actual blade. Consider that 
elliptical arc on the expanded area passing through 
Cy Be is its semi-minor axis, and since the angle 
c A B is its inclination when lying in its position 
on the actual blade to the axis of the intersecting 
cylinder, c A must be the length of its semi-major 
axis.^ Similarly AH, Aa, A6, &c., are the lengths of 
the semi-major axes of the elliptical arcs through 
H, a, ft, (fee, respectively, and B H, Ba, (fee, are the 
corresponding semi-minor axes. It follows at once 


that A is a focus of all these elliptical arcs, the other 
focus being at K where B K = B A. Draw, there- 
fore, through the points H, a, h^ &c., elliptical arcs 
with foci A, K and semi-major axes respectively 
equal to All, Aa, A6, &c. Then by the assump- 
tion, these elliptical arcs represent the helical arcs 
of intersection turned about B C till they lie in the 
same plane. If we reverse the process and turn 
them back from the expanded area through the 
same angle, their extremities will give us points 
on the outline of the blade. The angle any 
particular arc must be turned through is that 
which its pitch-line makes with B A. 

This enables us to draw the projections, and in 
dealing with these we shall take a particular one 
of the elliptical arcs and show how to obtain the 
projections of the point at one of its extremities ; 
tlie projections of the other extremity may be 
obtained in a similar way, but on the other side 
of the centre line. This will be a specimen arc. 
If the same method be adopted for the extremities 
of all the other arcs, series of points will be 
obtained, and if fair curves be drawn through 
the respective series, we have the required pro- 
jections. For each projection of the blade we 
shall therefore deal only with the projection of 
one .point on its outline. 

Take any one of the elliptical arcs as the speci- 
men, say that through c, viz. c, c Ca, Fig. 28, Plate 3. 
Draw C2 Co, parallel to the axis, mark off on the 



pitch-line through c, c CJg = ^o ^j- Draw c^ c^ per- 
pendicular to A B and c c^ parallel to it. Then 
CC4, is the projection of CqC2 on a fore and aft 
plane, and C3C4 is its projection on an athwartship 
plane. Set off CqC^ = C3C4, then ^5 is a point on 
the athwartship projection of the blade. Similarly 
on the other side of the arc we get another point 
c^j and so on for all the other arcs. 

It may be noticed that this projection may also 
be found thus; draw circular arcs with B as 
centre through H, «, ft, c, &c. On the blade the 
elliptical arc approximately coinciding with the 
helical arc will project on an athwartship plane 
into a circular arc, the chord of the- former of 
course projecting in that of the latter. Dealing 
with the arc through c, draw Co c^ parallel to the 
axis through Ca, meeting the circular arc in C5, then 
the elliptical arc c c^ will project on an athwart- 
ship plane into the circular arc c Cg. c^ is there- 
fore a point on the athwartship projection of the 

For the fore and aft projection take K P, Fig. 29, 
as the axis of the propeller, and draw P Q at right 
angles to it. Set off distances P H7, Pa^, P67, &c., 
respectively, equal to B Ho, Bag, Big, &c., and draw 
straight lines through the points H,, ay, &7, &c., 
parallel to K P. Dealing with the line c^ ۥ, Cg, 
set off CtCs equal to cc^j Fig. 28, then Cg is a 
point on the fore and aft projection of the blade. 
Similarly for other points. 


For tlie liorizoutal projection take N R, Fig. 30, 
as the axis, R being forward, and draw straight 
lines through N making angles with N R equal to 
H \ B, a A B, &c., Fig. 28, and inclining as 
shown since the blade is right-handed. These 
straight lines represent the directions on the actual 
blade of the chords of the ellij^tical arcs, the 
lengths are given in Fig. 28. Dealing with the 
line Nc*', which is the direction of the chord ^0^2* 
Fig. 28, mark off Ny = c^c^. Fig. 28, then y is a 
point on the horizontal projection. On the other 
side of N we get similarly y', the horizontal pro- 
jection of tlie other extremity of tlie chord. Simi- 
larly for other points. 

The complete projections of a three-bladed 
propeller are shown in Figs. 33, 34, 35, Plate 4. 
The athwartship projections of the two lower 
blades are simply repetitions of that of the upper 
blade, their centre lines being inclined to that of 
the upper one 5it angles of 120°, Fig. 33. 

The fore and aft projection of the lower blade. 
Fig. 34, is obtained thus : — Across the projections 
of the blades in Fig. 33 and the top blade of 
Fig. 34 draw straight lines at right-angles to their 
centre lines as in Figs. 28 and 29. Consider the 
point whose athwartship projection is c^ on the 
right-hand lower blade. Fig. 33 ; this being on the 
following edge will be abaft the centre line in 
Fig. 34, the corresponding point on the leading 
edge (ci) appearing on the forward side. 

G 2 


Then to obtain the position of this point on the 
fore and aft projection it must be borne in mind 
that it must lie in the same vertical plane perpen- 
dicular to the axis as it does when the blade is 
upright, and at the same distance from the hori- 
zontal plane through the axis as in it& athwartship 

Consider the point whose athwartship projection 
is t?2, Fig. 33. Draw C3C4, Fig. 34, on the left-hand 
side of the centre line P Q, parallel to the axis, at 
the same distance from it as Cj, Fig. 33, is from 
B P. Take c^c^ equal to CoC-t (c^ being the 
position on the fore and aft projection which the 
point would occupy if the blade were upright), 
then C4 is a point on the fore and aft projection of 
the right-hand lower blade. Similarly for other 

Proceed in a similar manner for the other lower 
blade, bearing in mind that the upper edge, 
Fig. 33, is here the leading or forward edge. The 
projection of one blade only is shown in Fig. 34 
to avoid confusion. 

In the horizontal projection of the lower blades. 
Fig. 35, we proceed similarly. The point whose 
athwartship projection is t?2, Fig. 33, for example, 
will appear on the after side of the centre line of 
the blade at a distance from it equal to CoCj, 
Fig. 34; and from the axis equal to the perpen- 
dicular distance of ("a* Fig. 33, from B E. 

The projections of a three-bladed propeller are 



thus completely determined. It may be remarked 
that it is often considered sufficient to replace the 
elliptical arcs on the expanded area, Fig. 28, by 
circular arcs with B as centre, forming the pro- 
jections from the chords of these arcs precisely as 
has been described for the elliptical ones. The 
error introduced by this method of procedure is 
not great, being only appreciable towards the root 
of the blade, where it is of little consequence. 

Blades are sometimes made with the generating 
line inclined to the iaxis, or in technical terms they 
are made with a skew. 
Let the two straight lines, 
AB, AC, Fig. 36, the 
former at right-angles 
to an axis, the latter 
inclined to A B at an 
angle a, moving together, 
generate screw surfaces 
of uniform and equal 
pitch. Then the helices 
of intersection of these 
two surfaces will be ex- 
actly similar, and one will be always a constant dis- 
tance from the other, this distance being at a radius 
Vj r tan a. Imagine these two surfaces so far 
similar, that when A C at any radius leaves the 
surface, A B at the same radius leaves its surface, 
then the expanded area of the surface so formed by 
A B will represent what may be termed the eflfec- 


tive expanded area of that formed by A C, and this 
should be of the elliptical or other form which 
would have been used if the generating line had 
been at right-angles to the axis. A blade generated 
by A C would therefore be formed from a blade 
generated by A B, simply by setting the helices of 
intersection, definite distances aft, the distance at 
M for example being M N. It follows therefore 
that the athwartsliip projection of the blade for the 
same " eflFective " expanded area is independent of 
the skew, and consequently for a skew blade with 
effective expanded area as for the blades shown in 
Figs. 33, 34, 35, the athwartsliip projection will 
be as in Fig. 33, no matter what the skew be. 

The fore and aft projection of tlie upper blade, 
Fig. 37, will be formed by using a centre line 
inclined to the vertical at an angle equal to the 
inclination of the generating line to tlie vertical, 
and proceeding as in Fig. 20, setting off the 
distances horizontally. The projections of the 
lower blades are determined in a similar way to 
that described for Fig. 34. For example, the 
point whose athwartsliip projection is c^, Fig. 33, 
will appear on Fig. 37 at C4, lying in the same 
vertical straight line as Ci {ct being the position 
of this point when the blade is upright), and being 
perpendicularly away from the axis, a distance 
equal to that of C2 from the horizontal plane 
through the axis. 

Next consider the horizontal projections. Fig. 38, 


For the top blade the pitch-lines are not all drawn 
through the same point as in Fig. 35, but each 
line is drawn at the corresponding angle to the 
axis through a point on the axis at a distance from 
Ml Ni (corresponding to M N in Fig, 37), equal to 
the distance of the corresponding point on the 
generating line P Q from M N, Fig. 37, the pro- 
cess then being as in Fig, 30. For the lower 
blade we proceed as in Fig. 35, for instance, the 
point (ca, Fig, 33) corresponding to C7, Fig, 37, 
when the blade is upright, will appear in Fig. 38 
at Cg at a distance from the axis equal to the 
distance of Cj, Fig. 33, from the vertical plane 
through the axis and from Mj Ni, equal to the 
distance of c^ from M N, Fig. 37. 

The projections of a three-bladed propeller with 
skew blades are shown in Figs. 33, 37, 38, except 
that the left-hand lower blade of Fig. 33 has not 
been shown in Fig. 37 to avoid confusion. 

Where the generating line is curved, the method 
is now obvious. 

Wo pass on to consider blades not of uniform 

If it is desired to make the pitch increase from 
the root of the blade towards the tip, that is, if the 
pitch at c. Fig. 28, for example, be 2 ttB Z instead 
of 2 TT B A, then the pitch-line at c will be Z c: 
instead of A c. With this modification the method 
of constructing the projections is the same. 

Blades are frequently made with an increasing 



pitch from leading to following edge. In Fig, 39, 

let the pitch at the leading edge at a radius equal 

c b 

be a 6, and suppose as we go to a point rf, 



the pitch increases to b e, then e c b will be the 
pitch-angle at this point. Similarly if at / the 

Fig. 30. " 

pitch increases to t(/, then bc(/ is the pitch-angle 
at/. Draw dh parallel to c^, and fk parallel to 
cg^ then if the curve of intersection at the radius 
under consideration be unrolled as in Fig. 27, 
instead of being straight it will be as adf—in 
other words, the pitch-line through a will not be 
straight ; if the pitch varies continually, then the 
pitch-line will be a continuous curve. 

A blade of uniformly varying pitch from lead- 
ing to following edge would be generated by a 
line always intersecting, and always inclined at 
the same angle to the axis, moving uniformly 


round the axis while advancing with uniform 
acceleration along it. 

Only the acting face of the blade preserves the 
helical form, the back being made to give the 
required thickness at the difiFerent parts. The thick- 
ness at the centre line of the blade is first fixed at 
root and tip, and set off from the face of the blade. 
The two points thus found being joined, the dis- 
tance of this line from the face gives the thickness 
at any intermediate point (see Fig. 29). The thick- 
ness at the tip should be as small as possible, con- 
sistent with good casting or forging, as the case 
may be, and in gun-metal is generally made about 
-^^ inch per foot of diameter. The blade when 
acting on the water is in the position of a beam 
under a load distributed all over its surface, 
varying in intensity, but it would be very difficult 
to find the bending moment at the root, and it is 
usual to make the rough assumptions that the total 
pressure on the blade tending to break it about the 
root section is proportional to the indicated thrust 


or to —Ty 
p K 

(where P = I.H.P. per blade ; 

p = the pitch of the propeller ; 

R = the revolutions per minute), 
also that the " leverage '* is proportional to D — rf, 
D being the diameter of the propeller, and d that 
of the boss ; and that the moment of inertia of the 
root section of breadth h and depth h is propor- 


tional to b h^, then h the required thickness at the 
middle of the root is obtained from the formula 

p . 11 . h 

the value of the coefficient c being about 230 for 
gun-metal, and 90 to 100 for forged steel blades. 
(In the above formula, /?, D, and d are to be 
taken in feet, and b and h in inches.) 

It is then usual to unroll the elliptical arc of 
Fig. 28 at any radius into a straight line, set off 
the thickness as found at its middle point, and 
describe a circular arc through the point so found 
and the extremities of the unrolled ellipse, and so 
obtain the thickness at other points than the 
middle (see Fig. 32). 

When tlje blades are made separate from the 
boss they are usually attached to it by bolts 
arranged in a bolt circle of diameter C inches. 
As the thickness of the metal at the root is not 
disposed symmetrically about the centre of the 
flange, it is convenient to put one more bolt on 
the after side than on the forward side, and as 
the after bolts take the ahead load, which is 
greater than the astern, it is also an advantageous 
arrangement. If B be the combined aiea in 
square inches of the bolts at the smallcist section 
(at the bottom of the thread) on tlie after side 
of the blade, k the distance of the c*entre of 
pressure of the blade from the under side of the 



flange in feet, R and P being as before, then 

B = ~7w5~' tli® coefficient K ranging in value 

from 18 to 21 for gun-metal. 

The number of bolts having been settled, their 
diameter is at once found. The bolts on the for- 
ward side are usually made of the same diameter 
for convenience. For the sake of possible adjust- 
ments that may be desirable on the trials of the 
machinery, and also for fining the pitch when it 
becomes necessary to reduce the steam pressure in 
the boilers, it is customary to make the bolt-holes 
in the blade-flange oval in order that the inclina- 
lion of the blades to the axis may be altered. The 
amount of the oval is determined thus. Fig. 40. 

Fig. 40. 

D E 

Let the true pitch of the blade be 2 tt C E, and let 
the desired range of pitch be 2 tt E B and 2 tt E D 
respectively, on each side of this pitch. Take a 


radius C A, so that A is about half-way up the 
Uade. Join A D, AE, A B, tlien if ^ be the angle 
DAB, the holes in the flange must be so elongated 

as to admit of the blade being turned through ^ 

on each side. 

The amount of the elongation on each side is 

therefore ^n) ' f = '^^^' ^ being measured in 


If the axis of the helices of intersection of the 
blade be originally that of the propeller shaft, 
the acting surface will not be truly helical about the 
centre line of the shaft when the blade is turned 
round as just described, as the pitch is not altered 
uniformly. There are only two sections of the 
blade which receive the same change of pitch, and 
tlicse are situated at the radii corresponding to a 
pitch angle of 45° in the case of the original and 
modified pitches respectively. Sections between 
these points receive a less change of pitch, and 
sections outside them a greater, in proportion to 
their distance from them. The effect produced 
therefore by twisting through any given angle 
depends upon the pitch-ratio ; if this is small the 
critical points are near the boss, and twisting 
to augment pitcli for example causes the pitch to 
increase throughout the greater part of the length 
of blade, the maximum occurring at the tip. If 
the pitcli-ratio be such tliat the critical points fall 


about the middle of tbe length, twisting to fine 
pitch will then result in a blade having the maxi- 
mum pitch in the centre. 

Figs. 29 and 31 show respectively longitudinal 
and transverse sections through tlie propeller boss. 




There are many reasons why a hydraulic propeller 
would be preferred to a screw or paddle in certain 
cases, if an economical result could be obtained 
with it, but tlie efficiency of the apparatus is 
necessarily so small that at the present moment it 
is believed that there is not a single vessel using 
the propeller for warlike or commercial purposes. 
When economy is a secondary consideration, and 
the circumstances are such as apparently to pre- 
clude the use of any propeller external to the 
vessel, the hydraulic propeller finds its opportunity. 
A steam lifeboat which has been recently built by 
Messrs. li. and H. G-reen of Blackwall for the 
National Lifeboat Institution, has been fitted with 
hydraulic machinery, made by Messrs. J. I. Thorny- 
croft and Co., and she has met with a considerable 
measure of success. It was considered that the 
difficulty of keeping a screw immersed, and the 
danger of its becoming fouled by wreckage, or 
injured upon a sandbank, rendered it unsuitable, 
and justified the introduction of a propeller which 
could never race, and which was much less liable 
to injury. 



The term jet-propeller, although in common use, 
is incorrect, the propeller in this system of pro- 
pulsion consisting of a pump within the vessel, 
which discharges jets of water in a stern ward 
direction, which are analogous to the race of a 
paddle or screw. 

In 18'<9 a hydraulic vessel called the Ilydro- 
motar was built in Germany from the designs of 
Dr. Fleischer. In this vessel the engine and 
pump were combined, the arrangement being as 
follows : — 

There was a cylinder lined inside with wood, at 
the bottom of which was a large pipe leading to a 
nozzle at the bottom of the vessel. A float of 
nearly the same diameter as the cylinder worked 
up and down in it. The cylinder being full of 
water and the float consequently at the top, steam 
was admitted by a valve above the float, and driv- 
ing it down ejected the water through the nozzle 
Fig. 41. On reaching the 
bottom of its stroke, the 
float opened the exhaust, 
and the steam passed 
into the condenser. The 
vacuum then created in 
the cylinder caused the 

water to rise partly 

through the nozzle, but 

principally through a suction-valve in the bottom 

of the condenser. The cylinder was thus filled 

Fig. 41. 



ZJ =^ 



with water, and the float rose to the top, in 
doing which it closed the exhaust and opened 
the steam-valve, and the operation was re- 
peated. The loss by condensation appears to 
have been less than might have been expected in a 
cylinder filled alternately with steam and water, 
but as the cylinder was not entirely emptied at 
each stroke, a layer of boiling water always re- 
mained at the top and adhered to the wooden 
linings as the float descended. The information 
published is unreliable as no proper raeasnrt;d mile 
trials were made. All calculations made from 
indicated horsepower cards are of little value in 
this system, as the loss between the boiler and the 
indicator, which must be very large, is thereby 

ignored. The only correct basis for comparison 
with either a screw or a turbine would be the 
amount of steam consumed per unit of work done. 
In 18CG, two armoured gunboats, the Viper and 
Watur^ntch, were built, the former being propelled 



by twin screws, and the latter by hydraalic 
machinery, designed by Mr. Ruthven. The 
Watenmtclta propeller consisted of a turbine 
14 feet indiameter, which drew water in at the 

bottom of the vessel, and discharged it through 
two 24rinch nozzles at the sides level with the 
water (see Figs. 42 and 43). 

In 1878, a hydraulic vessel was built by the 
Swedish Government for competition with a simi- 
lar vessel with twin screws. The hydraulic vessel 



was propelled by two turbines about 2 feet in 
diameter, which discharged water through sub- 
merged orifices at the sides near the extremities 
(see Figs. 44, 45, and 46). 

Fio. 45. 

Fio. 46. 

In 1883, Messrs. Thornycroft fitted one of a 
number of second class torpedo boats they were 
building for the British Admiralty with a hydraulic 
propeller consisting of a turbine 2 feet 6 inches in 
diameter, which discharged through two 9-inch 



nozzles at the sides above water (see Figs. 47 and 
48 and Plate 5), All these vessels were fully 

Fig. 47. 

Fio. 48. 

described by the author in a paper read before the 
Institution of Civil Engineers,* from which the 

* Proo. Inat. Civil Enginoors, Ixxvii. p. 1. 

II 2 


figures and Tables III. and IV., p. 104, giving a 
detailed comparison of the performance of the 
respective screw and turbine vessels, are taken. 
In every case a very notable difference was found 
between them, and always to the disadvantage of 
the latter. There appears to be a loss of power 
corresponding to about 50 per cent, experienced by 
the hydraulic propeller as compared with the screw. 
The causes of this loss are not hard to find. 

In the case of the Water witch and the Swedish 
boat, the water was received into the ship through 
a hole in the bottom in such a way as to suddenly 
arrest all the velocity which it had relatively to 
the vessel. In other words the entering water 
struck the ship and had the velocity of the ship 
impressed upon it before it entered the turbine. If 
the inlet is formed in the shape of a scoop, as was 
done in the Thornycroft boat (see Fig. 47) and 
Plate 5), and the water caused to change its direc- 
tion gradually without having its velocity relatively 
to the ship checked, then this cause of loss is 
avoided. In such a case, if the vessel were towed 
along with the turbine removed and replaced by 
a curved channel connecting the inlets and outlets, 
the water would be scooped up, and would flow out 
at the nozzles, leaving tbem, if they are not above 
the surface, with a velocity relative to the ship 
equal to the speed of the ship, and with no 
velocity relative to still water except such as would 
be imparted by the friction of the passages. 


The inlet of the Swedish vessel was subse- 
quently altered as shown in thick black lines in 
Fig. 44, and the partial scoop thus formed caused 
an increase of speed from 7 '87 knots to 8*12 
knots, with the same expenditure of power. 

Another loss of efficiency in the hydraulic system 
is due to the small area of stream acted upon, and 
the consequently high velocity which has to be 
imparted to it in order to give the necessary re- 
action (see p. 4). The reason why the area of stream 
acted upon is necessarily small, is that the size of 
the orifice which it is possible to make in a ship's 
bottom, is restricted by structural considerations, 
and must be very small indeed compared to the 
area of a screw's disc. Then again, the weight of 
water admitted into the ship is a serious considera- 
tion, as it represents so much loss of displacement. 

A further waste of power is caused by the 
friction of the water in the pipes and passages, 
and by the changes in direction of its flow in 
passing through the bottom and out through the 
sides in a fore and aft direction. For these reasons 
the hydraulic propeller is essentially wasteful. In 
the screw and turbine competitive Thornycroft 
torpedo boats, the efficiencies were found to be as 
follows:— Screw boat : engine, 0*77; screw pro- 
peller, • 65 ; total efficiency, • 5. Hydraulic 
boat : engine, 0*77; pump, 0*46; jet, 0*71; 
total efficiency, ' 254. 

The efficiencies of the pump and jet in this boat 


were measured by the author in the following 
manner : — 

A thin plate 1^ inch square was attached to 
the end of a thin lever and placed in the jet just 
where it left the nozzle. The pressure on this 
plate was recorded by a dynamometer attached to 
the end of the lever. By finding the pressure 
upon a similar lever without the plate, the eflFect of 
the portion of the lever immersed in the jet could 
be allowed for. The apparatus was so arranged 
that the pressure could be measured at every point 
of the jet and not in the centre only. From the 
pressures on the plate the velocity of the stream at 
diflFerent parts of the jet was estimated, and from 
the mean velocity, the quantity of water discharged 
was calculated. 

The relation between velocity of jet and pressure 
on the plate is as follows : — 

ProBSTire on plate 

• 627 X (area) x heaviness of fluid x (velocity)^ 


If W = weight of water discharged per 

second ; 
V = speed of vessel in feet per second ; 
S = true slip or acceleration, or addi- 
tional velocity impressed by the 
propelling apparatus in feet per 
V + S = velocity of discharge in feet per 

second ; 


g = acceleration produced by gravity 
in feet per second = 32*2; 


Then the theoretical efficiency of the jet = =. 

Efficiency of pump, supposing jet to have theo- 
retical efficiency and the engine an efficiency of 

Work stored up in water 
Effective H.P, of engine " 

Efficiency of pump and jet 

Useful work in jet 
Effective H.P of engine 

Total efficiency 

Useful work in jet 




I.H.P. X 650 

X 0-77 




LH.P. X 550 




Work expended LH.P. x 650 





O O O "** <0 00 
i-H <^ to 00 CO c^ 
iH CN CO O -^ 


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Ci iH C^ C^ iH iH 








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So f-H O i-H <M •** 

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oo o 


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to to iH 

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( 105 ) 



This propeller was the fruit of the study given to 
the subject of hydraulic propulsion by Mr. Thorny- 
croft, when designing the hydraulic torpedo boat 
already mentioned. 

It has been pointed out in the preceding chapter 
that there are four characteristics of the centri- 
fugal pump as applied for the purpose of pro- 
pelling vessels, which prevent it from competing 
successfully with the paddle or the screw. These 
are: — 

1, The diificulty of getting the water through 
the bottom of the vessel and into the pump without 
checking the velocity it already has relative to the 

2. The necessity of carrying in the vessel all the 
water acted upon. 

3. The loss caused by friction of the water in 
the pipes. 

4, The loss due to bends in the passages. 

It was obvious that if the turbine could be put 
outside the vessel and under the bottom, the first 
two causes of loss would be avoided, and also that 
if the water could be made to flow axially through 



the turbine instead of radially as in the Ruthven 
pump, no pipes would be needed, there would be 
no loss by changes of direction, and the friction 
would be reduced to that due to passage through 
the turbine alone. The propeller illustrated in 
Fig. 49 was therefore devised upon these lines, 

Fig. 49. 

and as it is neither a screw nor a turbine strictly 
speaking, although allied to both, it has received 
the name of the screw-turbine. 

It consists of a cylinder containing within it a 
body or boss of such a shape that the channel is 
gradually contracted from the forward to the after 
end. Within the forward part of the cylinder are 
placed revolving screw-blades attached to the 
forward part of the boss, which is in two portions. 

The pitch of the forward edge of the screw- 
blades multiplied by the number of revolutions is 
approximately equal to the velocity of feed ; the 
pitch increases uniformly along the length of the 
blade, imparting a uniform acceleration to the 
water. Aft of the revolving blades are placed 
numerous fixed blades of contrary curvature. The 


area of the channel through the propeller is so 
proportioned as to suit the acceleration of the water 
caused by the blades. Thus at the forward end is 
a large opening which will admit a certain quan- 
tity of water at the velocity of feed ; at the after 
end the area is restricted to that necessary to allow 
of the exit of the water at the speed of discharge. 
The long tapering body forming a prolongation of 
the boss outside of the cylinder, allows the streams 
of water to unite gradually without the formation 
of eddies. As the long pitch of the screw-blades 
causes considerable rotation of the water, the curved 
guides are so formed as to direct the water into a 
straight line aft, and the rotary motion is thus 
utilised without loss. When a model of this pro 
peller was experimented upon, the thrust of the 
revolving blades was measured separately from the 
thrust of the fixed guides. The latter was found 
to be quite considerable, amounting in the case of 
a very long pitch propeller to one-third of the 
total thrust. 

The efficiency of the screw-turbine was found by 
experiment to be at least equal to that of the 
common screw, and a given thrust can be obtained 
with a much less diameter. It is therefore a very 
suitable propeller for vessels of shallow draught. 
As the water is not accelerated at all before it 
reaches the propeller, that is, as there is no sucking 
action, there would appear to be less augmentation 
of hull resistance caused by the screw-turbine than 


by any form of open screw. It was stated on p, 21, 
that all open propellers work in a stream having a 

velocity varying between V + S and ^ + 9 

depending upon the greater or less rotation of the 
race, the eCFect of the guide-blades in combina- 
tion with the enclosed and contracted channel is 
to prevent rotation of the race, and to place the 
screw-turbiue in the same condition as an open 
propeller would be in if it were possible to imagine 
one which, like Mr. Fronde's " Acuator," produced 
no rotation. Its efficiency is therefore equal to 


Q, and the loss of work is the least possible. 

Were it not for the large surface exposed to 
friction, it might be expected to have a much 
higher efficiency than the common screw. 

It can be used with advantage, because of its 
relatively small diameter, in sea-going vessels, 
which often are in very light trim, and do not 
then properly immerse a common propeller, and 
therefore waste a large amount of power (see p. 34), 
and also in vessels in which the draught of water is 
so limited that the ordinary screw cannot be used. 
In such cases the screw-turbine possesses advan- 
tages as compared with paddle-wheels when high 
speed is required, because the weight of the 
machinery is much less than that of paddle engines 
of the same power, which necessarily run slowly. 


The arrangement shown in Plate 6 has 
proved very successful when the draught of water 
is small. The launch illustrated has a draught 
of 12 inches. A tunnel is formed in the bottom 
of the boat, the top of which rises above the sur- 
face, the ends being submerged. A 16-inch screw- 
turbine is placed in the tunnel, so that one-fourth 
of the diameter of the propeller is above the water- 
level when the boat is at rest, but as soon as it 
moves, water is drawn up into the tunnel, and the 
air expelled by the action of the propeller, which 
then works completely submerged. There is no 
loss of power in lifting the water 4 inches 
above the level of the surface, because in falling 
it gives out the work expended in raising it. 
There is an incidental convenience in this ar- 
rangement. An air-tight door can be placed at 
the crown of the tunnel immediately over the 
propeller, which can be opened from inside the 
boat, since the admission of air to the tunnel 
causes the water within it to fall to the level of the 
outside water surface, and leaves the propeller 
partially emerged. It can then be examined and 
cleared if it should have become fouled, and if 
there are twin screws this operation can be per- 
formed upon one propeller while the other is 
revolving slowly. 

Some vessels 140 feet by 21 feet, and having a 
draught of water of 1 foot 9 inches only, have 
been built upon this plan by Messrs. Thorny croft. 


They were propelled by twin screw-turbines 
32 inches diameter, and attained a speed of 

15 i knots per hour. A launch 56 feet long and 

16 inches draught of water has attained a speed 
of 16^ knots with one screw-turbine 20 inches in 

A smaller draught of water can be obtained 
by the use of this propeller than would be possible 
with the hydraulic propeller, on account of the 
excessive weight demanded by the latter for 
machinery and water. 



Air in screw race, 25, 34, 38 
AlectOy H.M.S., 6 
Antispire, 30 
Apparent slip, 14 
Archimedes, 25 
Auxiliary screws, 45 


Balancing screws, 35 

Bergen, 32 

Bevis screw, 45 

Blade area, 14, 65, 66, 78 

Blnff stem, effect of, 33 

British Association Beport on steering, 40 


Cargo steamers, screws for, 67 
Centrifugal action of screws, 25 
Collingwood^B screws, 16 
Constants for disc-area, 58 

Table of, 73 
Curves of efficiency, 57 

Dead water, 33 
Definitions, 12 
Diso-area, constants, 59, 73 

„ „ definition, 14 
Dundonald's screw, 25 
Dynamometer used in experiments, 55 

112 INDEX. 


Efficiency, affected by pitch-ratio, 61 
„ „ slip-ratio, 51 

„ causes of loss of, 4 
limitatioDS of, 3 

of hydraulic propeller, 101, 104 
Electric launches, screws for, 47 


Feathering screws, Bevis, 45 

Griffiths, 34 
White, 42 

FitzGerald's theory, 2 

Flat-bladed screws, 45 

Fleischer's Hydromotor^ 95 

»> »» 


GreenhiU's theory, 2 

Griffiths screw, 26 

„ self-adjusting screw, 34 
„ self-governing screw, 26 

Guide-blades, 28, 107 


Ilirsch screw, 27 
Howell torpedo screws, 47 
Hydraulic propeller, 4, 94 
HydromotoTj 95 


Immersion of screus, 25, 34, 78 
Inclined shaft, effect of, 35 
Increasing pitch, 13 


Jet propeller, see Hydraulic propeller. 

INDEX, 113 


Lateral motiou of storn caused by screw, 38 
,9 „ „ resisted by screw, 41 

LcDgtli of blade, 12 
Loss of efficiency, causes of, 4 


Mangin's screw, 27 
Models, how to make, 53 


Negative slip, 15, 64 


Oar efficiency, 3 
Overlai)ping screws, 47 


Paddle-wheels, 6 
Phant'^m ship, 58 

„ engine, 58 
Pitch, definition, 12 

„ how to estimate at sight, 24 
„ measurement of, 22 
„ virtual, 35 
Pitchometer, 21 
Position of screws, 32 
rropellers, balancing, 35 

Dundonald's, 25 
feathering, 34, 42, 45 
Fleischer's hydraulic, 95 
Griffiths', 26, 34 
guide-blade, 28, 107 
„ Hirsch's, 27 
„ hydraulic, 94 

„ Mapgin's, 27 



114 INDEX. 

Propellers, model, 51 
Rigg's, 28 
screw-turbine, 106 
Thomycroft's, 29 
Woodcroft's, 13 



Hacing, 37, 40 

Rankine's theory of propellers, 2, 3 

BatOer, 6 

Reaction, 1 

Reversing engines, effect of, 40 

Revolutions, average of paddle-wheels, 9 

Rigg's propeller, 28 

Rotatory motion of wake, 2, 21 

Rudder, twisted form of, 28 

Screw, sec Propeller 
Screw-turbine, 3, 105 
Shallow-draught steamers, lOD 
Slip, apparent, 14 

„ formula for, 15, 04 

„ negative, 15 

„ of paddle-wheels, 9 

„ real, 1 
Steering, effect of screws on, 38 
„ propeller, 42 

Teutonic's screws, 48 
Thorny croft's common screw, 20 
„ screw- turbine, 105 

Torpedo, screws for, 47 
Triple screws, 49 
Twin screws, 47 
Twisting blades in boss, CI, 02 
Tugs, screws for, 46 

INDEX. 115 

»» »> 

»» »> 


Varying pitch, 13, 16, 23, 27, 29, 87 
Vibration caused by inclined shaft, 37 

unequal speed of wake, 34 

turning, 41 
Viper, 96, 104 
Vortex theory, FitzGerald's, 3 


Wake correction, 58 

„ speed of, 33, 38 

„ values of, 74 
Watemiich, 96, 104 
White's feathering screw, 42 
Woodcroft's screw, 13 



Fiaxe 1. 





- — u 

-I — 


I — — 






Bate i. 


I — 


-- 4 


Plate 1. 




._ _^ 



-t- ■ — 1- 

.1 — 





1 ^ — 














































— " 




■ ■ 




/ / 

Fig 38 


















Qi <:i ^ 





-. I r 

4 : 

•^— » 



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■ i897- 



Applied Science 





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Electrical Testing. — A Handbook of Electrical 

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Electricity in the House. — Domestic Electricity 

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Household Manual. — Spons Household Manual : 

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House Hunting. — Practical Hints on Taking a 

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Hydraulic yidichmtvy .— Hydraulic Steam and 

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Sun Bath. 

Ice Making. — Theoretical and Practical Ammonia 

RefrigercUion^ a work of Reference for Engineers and others employed in 
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Indicator. — Twenty Years with the Indicator. By 

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Locomotive. — The Construction of the Modem 

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Liquid Fuel. — Liquid Fuel for Mechanical and 

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Mechanical Engineering. — Handbook for Me- 
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Metal Plate ^ot^.— Metal Plate Work: its 

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Boiler-makers and Plumbers. By C. T. Millis, M.I.M*£« Second 
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Metrical TbXA^s.— Metrical Tables. By Sir G. L. 

Molesworth, M.I.C.E. 32mo, doth, is, 6d, 

Mill-Gearing. — A Practical Treatise on Mill- Gear- 
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Mill - Gearing. — The Practical Millwright and 

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Mineral Oils. — A Practical Treatise on Mineral 

Oils and their By^ Products^ including a Short History of the Scotch Shale 
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Mining. — Economic Mining; a Practical Hand- 
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Perspective. — Perspective^ Explained and Illus^ 

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being interesting and instructive examples in Civile Alechanical^ Electrical^ 
Chemical^ Minings Military and Naval Engineering, graphically and 
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Engineering Profession and the Scientific Amateur, with chapters on 
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Plumbing. — Plumbings Drainage, Water Supply 

and Hot Water Fitting, By JOHN Smeaton, C.E., M.S.A., R.P., 
Examiner to the Worshipful Plumbers' Company. Numerous engravings, 
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Pumping Engines. — Practical Handbook on 

Direct-acting Pumping Engine and Steam Pump Construction, By 
Philip R. Bj<$rling. With 20 plates, crown 8vo, cloth, 5J. 

Pumps. — A Practical Handbook on Pump Con- 
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Principle of the action of a Pump— Classification of Pumps — Description of various 
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On designing Pump-buckets — Various Classes of ^ump-pistons — Cup-leathers — ^Air-vessels — 
Rules and Formulas, &c, &c. 

Pumps. — Pump Details. With 278 illustrations. 

By Philip R. Bjorling, author of a Practical Handbook on Pump 
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contents : 

Windbores— Foot-valves and Strainers — Clack-pieces, Budcet-door-pieces, and H'Pieces 
Working-barrels and Plunger-cases — Plungers or Rams — Piston and Plunger, Bucket and 
Plunger, Buckets and Valves — Pump-rods and Spears, Spear-rod Guides, &c. — Valve-swords, 
Spindles, and Draw-hooks — Set-ofis or Oflf-sets — Pipes, Pipe-joints, and Pipe-stay>— Pump- 
slmgs— Ouide-rods and Guides, Kites, Yokes, and Connectine-rods— L. Bdbs, T Bobs, 
Angle or V Bobo, and Balance-beams, Rock-^arms, and Fend-o£f Beams, Cistern^ and Tanks 
— Minor Details. 

Pumps. — Pumps and Pumping Machinery. By 

F. CoLVSR, Mem. Inst C.E., Mem. Inst M.£. Part I., second edition, 
revised and enlarged, with 50 plates, 8vo, cloth, i/. &r. 

Three-throw Lift and Well Pumps— Tonkin's Patent ** Combh " Steam Pump— Thome- 
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Horizontal High-pressure Eiuines — Horizontal Compound Engines— Reidler Engine— Ver* 
tical Compound Pumping Engines — Compound Beam Pumpmg Ennnes — Shonheyder's 
Patent Regulator — Comisn Beam Engines — ^Worthington High-^uty Pumping Engine- 
Davy's Patent Differential Pumping Engine — Tonkin's Patent Pumping Engine— Lancashire 
Boiler— Babcock and Wilcox Watex^tube BoUers. 


Pumps. — Pumps, Historically, Theoretically, and 

Practically Considered, By P. R. BjoRLlNG. With 156 illustrations. 
Crown 8vo, cloth, yj. 6</. 

Quantities. — A Complete Set of Contract Documents 

far a Country Lodge^ comprising Drawings, Specifications, Dimensions 
(for quantities), Abstracts, Bill of Quantities, Form of Tender and Con- 
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Quantity Surveying. — Quantity Surveying. By 

J. Leaning. With 68 illustrations. Third edition, revised, demy 8vo, 

cloth, 1 5 J. 


A complete Explanation of the London I Schedule of Prices. 

Practice. Form of Schedule of Prices. 

General Instructions. Analysis of Schedule of Prices. 

Order of Taking Off. I Adjustment of Accounts. 

Modes of Measurement of the varioiu Trades. > Form of a Bill of Variations. 
Use and Waste. 
Ventilation and Warming. 
Credits, with various Examples of Treatment. 

Remarks on Specifications. 
Prices and Valuation of Work, with 
Examples and Remarks upon each Trade. 

Abbreviations. ^ ! The Law as it affects Quantity Surveyors, 

Squaring^ the Dimensions. | with Law Reports. 

Abstracting, with Examples in illustration of , Taking Off after the Old Method. 

each Trade. Northern Practice. 

Billing. I llie General Sutement of the Methods 

Examples of Preambles to each Trade. | recommended by the Manchester Society 

Form for a Bill of Quantities. j of Architects for taking Quantities. 

Do. Bill of Credits. Examples of Collections. 

Do. Bill for Alternative Estimate. 1 Examples of '* Taking Off" in each Trade. 

Restorations and Repairs, and Form of BilL I Remarks on the Past and Present Methods 

Variations before Acceptance of Tender. ^ of Estimating. 

Errors in a Builder's Estimate. { 

Railway Curves. — Tables for Setting out Curves 

for Railways^ Canals^ Roads^ etc,^ varying from a radius of five chains 
to three miles. By A. Kennedy and R. W. Hackwood. Illustrated^ 
32mo, cloth, 2J. td 

Roads. — The Maintenance of Macadamised Roads. 

By T. CODRINGTON, M.I.C.E., F.G.S., General Superintendent of 
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Scamping Tricks. — Scamping Tricks and Odd 

Knowledge occasionally practised upon Public Works^ chronicled from the 
confessions of some old Practitioners. By John Newman, Assoc. M. 
Inst. C.E., author of * Earthwork Slips and Subsidences upon Public 
Works,* * Notes on Concrete,* &c. Crown 8vo, cloth, 2s. 6d, 

Screw Cutting. — Turners Handbook on Screw 

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Formulae. By Walter Price. Fcap 8vo, cloth, is. 


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Engineer. Second edition, oblong, doth, is. 

Sewerage. — Sewerage and Sewage Disposal. By 

Henry Robinson, Mem. Inst. C.E., F.G.S., Professor of Civil 
Engineering, King's College, London, &c., with large folding plate. 
Demy 8vo, cloth, 12s. 6d, 

Slide Valve. — A Treatise on a Practical Method 

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various forms of Plain Slide- Valve and Expansion Gearing ; together with 
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Soap. — A Treatise on the Manufacture of Soap and 

Candles, Lubricants and Glycerine. By W. Lant Carpenter, B.A., 
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Stair Building. — Practical Stair Building and' 

Handrailing by the Square Section and Falling Line System, By W. H. 
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Steanl Boilers. — Steam Boilers^ their Manage- 
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Steam Engine. -^ A Practical Treatise on the 

Steam Engine^ containing Plans and Arrangements of Details for Fixed 

Steam Engines, with E^ys on the Principles involved in Design and 

Construction. By Arthur Rigg, Engineer, Member of the Society of 

Engineers and of the Royal Institution of Great Britain. Demy 4to, 

copiously illustrated with woodcuts and 103 plates, in one Volume* 

Second edition, cloth, 25J. 

This work is not, in any sense, an elementary treatise« or history of the steam engine, but 
Is intended to describe examples of Fixed Steam Engines without entering into the wide 
domain of locomotive or marine practice. To this end illustrations will be given of the most 
recent arrangements of Horisontal, Vertical. Beam, Pumfung, Winding, Portable, Semi- 
portable, Cortiss, Allen, Compound, and other similar Engines, by the most eminent Firms in 
ureat Britain and America. ^ The laws relating to the action and precautions to be observed 
in the construction of the varoiu details, such as Cylinders, Pistons, Piston-rods, Connecting- 



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Steam Engine. — The Steam Engine considered as 

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Steam Engine. — Steam Engine Management ; a 

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Steam Engine. — A Treatise on Modem Steam 

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Sugar. — Tables for the Quantitative Estimation of 

the Sugars^ with Explanatory Notes. By Dr. Ernest Wein ; translated, 
with additions, by William Frew, Ph.D. Crown 8vo, cloth, 6x. 

Sugar. — A Handbook for Planters and Refiners ; 

being a comprehensive Treatise on the Culture of Sugar-yielding Plants, 
and on the Manufacture, Refining, and Analysis of Cane, Palm, Maple, 
Melon, Beet, Sorghum, Milk, and Starch Sugars ; with copious 
Statistics of their Production and Commerce, and a chapter on the 
Distillation of Rum. By C. G. Warnford Lock, F.L.S., &c. ; 
B. E. R. Newlands, F.C.S., F.I.C., Mem. Council Soc. Chemical 
Industry ; and J. A. R. Newlands, F.C.S., F.I.C. Upwards of 200 
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Surveying. — A Practical Treatise on the Science of 

Land and Engineering Surveyings Levelling^ Estimating Quantities, etc.^ 
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Surveying and Levelling. — Surveying and 

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Tables of Logarithms! — A B C Five-Figure 

Logarithms for general use. By C. J. Woodward, B.Sc Containing 
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Telephones. — Telephones, their Construction and 

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Tropical Agriculture. — Tropical Agriculture: a 

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principal Products of the Vegetable Kingdom. By P. L. SiMMONDS, 
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Turning. — The Practice of Hand Turning in Wood, 

Ivory, Shelly etc,, with Instructions for Turning such Work in Metal as 
may be required in the Practice of Turning in Wood, Ivory, etc ; also 
an Appendix on Ornamental Turning. (A book for beginners.) By 
Francis Campin. Third edition, with wood engravings, crown Svo, 
cloth, 3x. 6d, 

Valve Gears. — Treatise on Valve- Gears, with 

special consideration of the Link-Motions of Locomotive Engines. By 
Dr. GusTAV Zeuner, Professor of Applied Mechanics at the Confede- 
rated PoljTtechnikum of Zurich. Translated from the Fourth German 
Edition, by Professor J. F. Klein, Lehigh University, Bethlehem, Pa, 
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Varnish. — The practical Polish and Varnish-Maker ; 

a Treatise containing 750 practical Receipts and Formulae for the Manu- 
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workers in Wood and Metal, and directions for using same. By H. C. 
Standage (Practical Chemist), author of 'The Artist's Manual of 
Pigments.' Crown Svo, cloth, ts, 

B 2 


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ing; or, Ventilation with Warm Air by Self-acting Suction Power. 
With Review of the Mode of Calculating the Draught in Hot-air Flues, 
and with some Actual Experiments by T. Drysdals, M.D., and J. W. 
Hayward, M.D. With plates and woodcuts. Third edition, with some 
New Sections, and the whole carefully revised, 8vo, cloth, 7^. 6^ 

Warn\ing and Ventilating. — A Practical 

Treatise upon Warming Buildings by Hot Water^ and upon Heat and 
Heating Appliances in general ; with an inquiry respecting Ventilation, 
the cause and action of Draughts in Chimneys and Flues, and the laws 
relating to Combustion. By Charles Hood, F.R.S. Re-written by 
Frederick Dye. Third edition. 8vo, cloth, 15/. 

Watchwork. — Treatise on Watchwork, Past and 

Present, By the Rev. H. L. Nelthropp, M.A., F.S.A. With 32 
illustrations^ crown 8vo, cloth, dr. td, 


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up — The Verge — ^The Horizontal— The Duplex— The Lever— The ChroncHnetei^— Repeating 
Watches— Keyless Watches— The Pendulum, or Spiral Spring— Compensation— Jewelling of 
Pivot Holes— Oerkenwell — Fallacies of the Trade — Incapacity of Workmen— How to Choose 
and Use a Watch, etc. 

Water Softening. — Water Softening and Purifi- 
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Harold Collet. Crown 8vo, cloth, ^s. 

Waterworks. — T/ie Principles of Waterworks 

Engineering, By J. H. Tudsbery Turner, B.Sc, Hunter Medallist 
of Glasgow University, M. Inst C.E., and A. W. Brightmore, M.Sc, 
Assoc. M. Inst. C.E. With illustrations, medium 8vo, cloth, 251. 

Well Sinking. — Well Sinking. The modern prac- 
tice of Sinking and Boring Wells, with geological considerations and 
examples of Wells. By Ernest Spon, Assoc. Mem. Inst. C.K 
Second edition, revised and enlarged. Crown Svu, cloth, los, 6d, 

Wiring. — Incandescent Wiring Hand-Book. By 

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Teohnloal Terms in Frenoh, German, Italian, and Spanish. 

In 97 numbers, Super-royal Svo, containing 3132 printed pages and 7414 
engravings. Any number can be had separate : Nos. i to 95 is, each, 
post free ; Nos. 96, 97, 2x., post free. 

Adhesion .. 
Agricultural Engines 
Air-Pump .. 
Algebraic Signs .. 


Amalgamating Machine 
Anchors .. 
Angular Motion . . 
Angle of Friction . . 
Animal Charcoal Machine 
Antimony, 4 ; Anvil 
Aqueduct, 4 ; Arch 
Archimedean Screw 
Arming Press 
Armour, 5 ; Arsenic 
Artesian Well 
Artillery, 5 and 6 ; Assay 
Atomic Weights .. 
Auger, 7 ; Axles . . 
Baknce, 7 ; Ballast 
Bank Note Machinery 
Bam Machinery .. 
Barker's Mill 
Barometer, 8 ; Barracks 

Complete List of all the Subjects : 

Barrage .. .. 




and 2 


2 and 3 

3 and 4 
.. 3 
.. 3 
.. 4 

.. 4 
.. 4 

.. 4 

4 and 5 

.. 5 

.. 5 
.. 6 

6 and 7 

.. 7 
.. 7 

.. 7 

7 and 8 

.. 8 
.. 8 

.. .. ..8 and 9 

Battery 9 and 10 

Bell and Bell-hanging .. ..10 
Belts and Belting .. ..10 and 1 1 

Bismuth .. .. .. ., 11 

Blast Furnace 
Blowin<; Machine 
Body Plan.. 

Bond . . • • 

Bone Mill .. 
Boot-making Machinery 
Boring and Blasting 

Bread Machine 
Brewing Apparatus 
Brick-making Machines 

Cam, 29; Canal .. 

Cement, 30 ; Chimney 
Coal Cutting and Washing Ma- 
chinery .. ., .. .. 31 

Coast Defence .. .. 3i» 32 

Compasses.. .. .. ..32 

Construction .. ..32 and 33 

Cooler, 34; Copper .. ••34 
Cork-cutting Machine .. ••34 

11 and 12 

.. 12 

12 and 13 

13. I4» 15 
15 and 16 

.. 16 

.. 16 

16 to 19 

19 and 20 

.. 20 

20 and 21 

.. 21 

21 to 28 

.. 28 

28 and 29 


29 and 30 






Cotton Machinery 

Damming .. 

Details of Engines 


Distilling Apparatus 

Diving and Diving Bells 


Drainage .. 


Dredging Machine 



Engines, Varieties 

Engines, Agricultural 

Engines, Marine .. 

Engines, Screw .. 

Engines, Stationary 


Fan > • . . 

File-cutting Machine 

Fire-arms .. 

Flax Machinery .. 

Float Water-wheels 


Founding and Casting 

Friction, 50 ; Friction, Angle of 3 

Fuel, 50; Furnace .. 50, 51 

Fuze, 51 ; Gas .. .. .. 51 

Gearing .. .. .. 51, 52 

Gearing Belt .. .. 10, 1 1 

Geodesy .. .. .. 52 and 53 

Glass Machinery .. .. •• 53 

Gold, 53, 54 ; Governor . . . . 54 

Gravity, 54 ; Grindstone .. 54 

Gun-carriage, 54; Gun Metal .. 54 
Gunnery .. .. .. 54 to 56 

34 and 35 

.. 35 
35 to 37 


.. 38 

38 and 39 

39 and 40 

40 and 41 
.. 41 
.. 41 

41 to 43 
43» 44 

I and 2 

74, 75 

45, 46 
.. 46 
.. 46 



.. 48 

.. 48 

48 to 50 


Gun Machinery .. 

Hand Tools 

Hanger, 58 ; Harbour 

Haulage, 58, 59 ; Hinging 

Hydraulics and Hydraulic Ma 




.. 58 


Ice-making Machine 
Indicator .. 

Iron Ship Building 
Irrigation .. 

59 to 63 
.. 63 
.. 63 
. . 63 and 64 
. • 64 
.. 64 to 67 
.. ,. 67 

. . 67 and 68 


Isomorphism, 68 ; Joints .. 68 

Keels and Coal Shipping 68 and 69 
Kiln, 69 ; Knitting Madiine .. 69 
Kyanising .. •. .. . •• 69 

Lamp, Safety .. .. 69, 70 

Lead .. .. .. .. jo 

Lifts, Hoists .. .. 70, 71 

Lights, Buoys, Beacons .. 71 and 72 
Limes, Mortars, and Cements .. 72 
Locks and Lock Gates .. 72, 73 
Locomotive .. ., -.73 

Machine Tools .. .. 73, 74 

Manganese .. .. ••74 

Marine Engine .. •'74 and 75 

Materials of Construction 75 and 76 
Measuring and Folding . . . . 76 

Mechanical Movements .. 76, 77 
Mercury, 77; Metallurgy .. 77 

Meter .. .. .. 77, 78 

Metric System .. .. ..78 

Mills .. .. .. 78, 79 

Molecule, 79 ; Oblique Arch .. 79 
Ores, 79, 80 ; Ovens .. ..80 

Over-shot Water-wheel .. 80, 81 
Paper Machinery . . .. ..81 

Permanent Way .. .. 81, 82 

Piles and Pile-driving . . 82 and 83 
Pipes .. .. .. 83, 84 

Planimeter .. .. ..84 

Pumps . . . . . . 84 and 85 

Quarrying .. .. .. ..85 

Railway Engineering .. 85 and 86 
Retaining Walls .. .. ..86 

Rivers, 86, 87 ; Riveted Joint .. 87 

Roads 87, 88 

Roofs .. .. .. 88, 89 

Rope-making Machinery .. 89 

Scaffolding .. .. ..89 

Screw Engines .. .. 89, 90 

Signals, 90; Silver .. 90» 91 

Stationary Engine .. 91, 92 

Stave-making & Cask Machinery 92 
Steel, 92 ; Sugar Mill . . 92, 93 
Surveying and Surveying Instru- 
ments .. .. .. 93, 94 

Telegraphy .. .. 94» 95 

Testing, 95 ; Turbine .. ••95 

Ventilation .. 95, 96, 97 

Waterworks ,. .. 96, 97 

Wood-working Machinery 96, 97 
Zinc .. ,, .. 96, 97 


In Mipar-royal 8vob iz68 pp^ wiiA S400 HlmtirmUoiu^ in 3 'Divisions, doth, price i^ 6d* 

•ach ; or x vol., doth, •L ; or half-morocco, a/. 8f . 




Edited by ERNEST SPON, Mxmb. Soc. Enginkbks. 

Abacus, Counters, Speed 
Indicators, and Slide 

Agricoltnral Implements 
and Machinery. 

Air Compressors. 

Animal Charcoal Ma- 


Axles and Axle-boxes. 

Bam Machinery. 

Belts and Belting. 

Blasting. Boilers. 


Brick Machinery. 


Cages for Mines. 

Calcnlos, Differential and 



Cast Iron. 

Cement, Concrete, 
Limes, and Mortar. 

Chimney Shafts. 

Coal Cleansing and 

Coal Mining. 

Coal Cutting Machines. 

Coke Ovens. Copper. 

Docks. Drainage. 

Dredging Machinery. 

Djmamo • Electric and 
Magneto-Electric Ma- 


Electrical Engineering, 
Telegraphy, Electric 
Lighting and its prac- 
tical details,Telephones 

Engines, Varieties of. 

Explosives. Fans. 

Founding, Moulding and 
tlie practical work of 
the Foundry. 

Gas, Manufacture of. 

Hammers, Steam and 
other Power. 

Heat Horse Power. 



Indicators. Iron. 

lifts, Hoists, and Eleva- 

Lighthouses, Buoys, and 

Machine Tools. 

Materials of Const 


Ores, Machinery and 
Processes employed to 


Pile Driving. 

Pneumatic Transmis- 



Road Locomotives. 

Rock Drills. 

Rolling Stock. 

Sanitary Engineering. 



Steam Navvy. 

Stone Machinery. 


Well Sinking. 


In demy 4to, handsomely bound in cloth, illustrated with 220 Jull page plates^ 

Price 1 5 J. 





Containing aao Plates, with numerous Drawings selected from the Architectone 

of Former and Present Times. 

7%€ Details and Designs are Drawn to Scale, J", \'\ J", and Full siae 

keing chiefly used. 

The Plates are arranged in Two Parts. The First Part contains 
Details of Work in the four principal Building materials, the following 
being a few of the subjects in this Part : — ^Various forms of Doors and 
Windows, Wood and Iron Roofs, Half Timber Work, Porches, 
Towers, Spires, Belfries, Flying Buttresses, Groining, Carving, Church 
Fittings, Constructive and Ornamental Iron Work, Classic and Gothic 
Molds and Ornament, Foliation Natural and Conventional, Stained 
Glass, Coloured Decoration, a Section to Scale of the Great Pyramid, 
Grecian and Roman Work, Continental and English Gothic, Pile 
Foimdations, Chimney Shafts according to the regulations of the 
London County Council, Board Schools. The Second Part consists 
of Drawings of Plans and Elevations of Buildings, arranged under the 
following heads : — Workmen's Cottages and Dwellings, Cottage Resi- 
dences and Dwelling Houses, Shops, Factories, Warehouses, Schools, 
Churches and Chapels, Public Buildings, Hotels and Taverns, and 
Buildings of a general character. 

All the Plates are accompanied with particulars of the Work, with 
Explanatory Notes and Dimensions of the various parts. 

Spedmen Paga, rtdutidjivm Iht origimalt. 



Crown 8yo, doth, 485 pages, with illustrations, St, 



Synopsis of Contents. 

Addimetry and Alkali- 
Boiler Incrustations. 
Cements and Lutes. 


Dyeing, Staining, and 

Gelatine, Glue, and Size. 

Hydrogen peroxide. 



Ivory substitutes. 


Luminous bodies. 





Perchloric add. 

Potassium oxalate. 


Pigments, Paint, and Painting : embracing the preparation of 
Pignunts, induding alumina lakes, blacks (animal, bone, Frankfort, ivory, 
lamp, sight, soot), blues (antimony, Antwerp, cobalt, caeruleum, Egyptian, 
manganate, Paris, Peligot, Prussian, smalt, ultramarine), browns (bistre, 
hinau, sepia, sienna, umber, Vandyke), greens (baryta, Brighton, Brunswick, 
chrome, cobalt, Douglas, emerald, manganese, mitis, mountain, Prussian, 
sap, Scheele's, Schwemfurth, titanium, verdigris, zinc), reds (Brazilwood lake, 
carminated lake, carmine, Cassius purple, cobalt pink, cochineal lake, colco- 
thar, Indian red, madder lake, red chalk, red lead, vermilion), whites (alum, 
baryta, Chinese, lead sulphate, white lead — by American, Dutch, French, 
German, Kremnitz, and Pattinson processes, precautions in making, and 
composition of commercial samples — whiting, Wilkinson's white, zinc white), 
yellows (chrome, eamboge, Naples, orpiment, realgar, yellow lakes) ; Paint 
(vehides, testing oils, (uiers, grinding, storing, applying, priming, drying, 
filling, coats, brushes, surface, water-colours, removmg smell, discoloration ; 
miscellaneous paints — cement paint for carton-pierre, copper paint, gold paint, 
iron paint, lime paints, silicated paints, steatite paint, transparent paints, 
tungsten paints, window paint, zinc paints) ; Painting (general instructions, 
proportions of ingredients, measuring paint work ; carriage painting — priming 
paint, best putty, finishing colour, cause of cracking, mixing the paints, oils, 
driers, and colours, varnishing, importance of washing vehicles, re-vamishing, 
how to dry paint ; woodwork painting). 


Crown 8vo, doth, 480 pages, with 183 illustrations, 5/. 



Uniform with the First and Second Series* 

Synopsis of Coktents. 





Iron and SteeL 



Lacquers and Lacquering. 



































Enamels and Glazes. 
















Electrics, — Alarms, Bells, Batteries. Carbons, Coils, Dynamos, Micro- 
phones, Measuring, Phonographs, Telephones, &a, 130 pp., 112 iUustrattons. 

^ t 





250 niuitratioiii, with Complete Index, and a General Index to the 

Four Seriei, 6i. 

Waterproofing — rubber goods, cuprammonium processes, miscellaneoos 

Packing and Storing articles of delicate odour or colour, of a deliquescent 
character, liable to ignition, apt to suffer from insects or damp, or easily 

Embalming and Preserving anatomical specimens. 

Leather Polishes. 

Cooling Air and Water, producing low temperatures, making ice, cooling 
syrups and solutions, and separating salts from liquors by refrigeration. 

Pumps and Siphons, embracing every useful contrivance for raising and 

supplying water on a moderate scale, and moving corrosive, tenacious, 

and other liquids. 
Desiccating — air- and water-ovens, and other appliances for drying natural 

and artificial products. 
Distilling — water, tinctures, extracts, pharmaceutical preparations, essences, 

perfumes, and alcoholic liquids. 

Emulsifying as required by pharmacists and photographers. 

Evaporating — saline and other solutions, and liquids demanding special 

Filtering — water, and solutions of various kinds. 

Percolating and Macerating. 


Stereotyping by both plaster and paper processes. 

Bookbinding in all its details. 

Straw Plaiting and the fabrication of baskets, matting, etc 

Musical Instruments — the preservation, timing, and repair of pianos, 
harmoniums, musical boxes, etc 

Clock and Watch Mending — adapted for intelligent amateurs. 

Photography — recent development in rapid processes, handy apparatus, 
numerous recipes for sensitizing and developing solutions, and applica- 
tions to modem illustrative purposes. 


Crown 8vo, cloth, with 373 illustrations, price Ss» 



Containing many new Articles, as well as additions to Articles included in 

the previous Series, as follows, viz. : — 


Barometers, How to make. 

Boat Building. 

Camera Lucida, How to use. 

Cements and Lutes. 



Corrosion and Protection of Metal 

^ Surfaces. 

Dendrometer, How to use. 


Diamond Cutting and Polishing. Elec- 
trics. New Chemical Batteries, Bells, 
Commutators, Galvanometers, Cost 
of Electric Lighting, Microphones, 
Simple Motors, Phonogram and 
Graphophone, Registering Appa- 
ratus, Regulators, Electric Welding 
and Apparatus, Transformers. 




Fireproofing, Buildings, Textile Fa- 

Fire-extinguishing Compounds and 

Glass Manipulating. Drilling, Cut- 
ting, Breaking, Etching, Frosting, 
Powdering, &c. 

Glass Manipulations for Laboratory 

Labels. Lacquers. 
Illuminating Agents. 
Inks. Writing, Copying, Invisible, 

Marking, Stamping. 
Magic Lanterns, their management 

and preparation of slides. 
Metal Work. Casting Ornamental 

Metal Work, Copper Welding 

Enamels for Iron and other Metals, 

Gold Beating, Smiths* Work. 
Modelling and Plaster Casting. 

Packing and Storing. Acids, &c. 
Preserving Books. 
Preserving Food, Plants, &c. 
Pumps and Syphons for various 

Repairing Books. 
Rope Tackle. 
Taps, Various. 
Tobacco Pipe Manufacture. 
Tying and Splicing Ropes. 
Velocipedes, Repairing. 
Walking Sticks. 


In demy 8vo, cloth, 600 pages and 1420 illustrations, 6s. 




Mechanical Drawing — Casting and Founding in Iron, Brass, Bronze, 
and other Alloys — Forging and Finishing Iron — Sheetmetal Working 
^Soldering, Brazing, and Burning — Carpentry and Joinery, embracing 
descriptions of some 400 Woods, over 200 Illustrations of Tools and 
their uses, Explanations (with Diagrams) of 116 joints and hinges, and 
Details of Construction of Workshop appliances, rough furniture, 
Garden and Yard Erections, and House Building — Cabinet-Making 
and Veneering — Carving and Fretcutting — Upholstery — Painting, 
Graining, and Marbling — Staining Furniture, Woods, Floors, and 
Fittings — Gilding, dead and bright, on various grounds — Polishing 
Marble, Metals, and Wood — ^Varnishing — Mechanical movements, 
illustrating contrivances for transmitting motion — ^Turning in Wood 
and Metals^Masonry, embracing Stonework, Brickwork, Terracotta 
and Concrete — Roofing with Thatch, Tiles, Slates, Felt, Zinc, &c. — 
Glazing with and without putty, and lead glazing — Plastering and 
Whitewashing — Paper-hanging — Gas-fitting — Bell-hanging, ordinary 
and electric Systems — Lighting — Warming — Ventilating — Roads, 
Pavements, and Bridges — Hedges, Ditches, and Drains — Water 
Supply and Sanitation —Hints on House Construction suited to new 

E. & F. N. SPON, Limited, 126 Strand, London.